Latency reduction techniques in wireless communications

ABSTRACT

Methods, systems, and devices for wireless communication are described that provide for reduced timing between certain downlink communications and responsive uplink communications relative to certain legacy systems (e.g., legacy LTE systems). A user equipment (UE) or base station may be capable of operating using two or more timing configurations that each include an associated time period between receipt of a downlink communication (e.g., a grant of uplink resources or shared channel data) and a responsive uplink communication (e.g., an uplink transmission using the granted uplink resources or feedback of successful reception of the shared channel data). In cases where a UE or base station are capable of two or more timing configurations, a timing configuration for a transmission may be determined and the responsive uplink communication transmitted according to the determined timing configuration.

CROSS REFERENCES

The present Application for Patent is a Continuation of U.S. patentapplication Ser. No. 15/642,104 by Chen, et al., entitled “LATENCYREDUCTION TECHNIQUES IN WIRELESS COMMUNICATIONS” filed Jul. 5, 2017,which claims the benefit of U.S. Provisional Patent Application No.62/360,194, entitled “LATENCY REDUCTION TECHNIQUES IN WIRELESSCOMMUNICATIONS,” filed Jul. 8, 2016, and to U.S. Provisional PatentApplication No. 62/368,716, entitled, “LATENCY REDUCTION TECHNIQUES INWIRELESS COMMUNICATIONS,” filed Jul. 29, 2016, assigned to the assigneehereof.

BACKGROUND

The following relates generally to wireless communication and morespecifically to latency reduction techniques in wireless communications.

Wireless communications systems are widely deployed to provide varioustypes of communication content such as voice, video, packet data,messaging, broadcast, and so on. These systems may be capable ofsupporting communication with multiple users by sharing the availablesystem resources (e.g., time, frequency, and power). Examples of suchmultiple-access systems include code division multiple access (CDMA)systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, and orthogonal frequencydivision multiple access (OFDMA) systems, (e.g., a Long Term Evolution(LTE) system). A wireless multiple-access communications system mayinclude a number of base stations, each simultaneously supportingcommunication for multiple communication devices, which may be otherwiseknown as user equipment (UE).

In some instances, transmission errors between mobile devices and basestations are avoided and/or corrected by utilizing an automatic repeatrequest (ARQ) scheme. An ARQ scheme may be employed to detect whether areceived packet is in error. For example, in an ARQ scheme, a receivermay notify a transmitter with a positive acknowledgment (ACK), when apacket is received free from errors; and the receiver may notify thetransmitter with a negative acknowledgment (NACK), if an error isdetected. A hybrid ARQ (HARQ) scheme may be used to correct some errorsand to detect and discard certain uncorrectable packets. In somescenarios, however, the overall HARQ delay may cause certaininefficiencies in wireless communications.

Furthermore, in some cases uplink resources may be allocated to a UE indownlink control information that is transmitted in a downlinktransmission from a base station to the UE. The UE may receive thedownlink control information, decode the allocated uplink resources, andbegin transmitting the associated uplink transmission following acertain time period from a transmission containing the downlink controlinformation. The delay from the reception of the downlink allocation toa start of uplink transmissions may also cause certain inefficiencies inwireless communications.

SUMMARY

The described techniques relate to improved methods, systems, devices,or apparatuses that support latency reduction techniques in wirelesscommunications. Generally, the described techniques provide for reducedtiming between certain downlink communications and responsive uplinkcommunications relative to certain legacy systems (e.g., legacy LTEsystems). In some examples, a user equipment (UE) or base station may becapable of operating using two or more timing configurations that eachinclude an associated time period between receipt of a downlinkcommunication (e.g., a grant of uplink resources or shared channel data)and a responsive uplink communication (e.g., an uplink transmissionusing the granted uplink resources or feedback of successful receptionof the shared channel data). In cases where a UE or base station arecapable of two or more timing configurations, a timing configuration fora transmission may be determined and the responsive uplink communicationtransmitted according to the determined timing configuration. In caseswhere a reduced time period is used for transmissions, latency of thesystem may be reduced and the efficiency of the system enhanced.

A method of wireless communication is described. The method may includedetermining whether to use a first timing configuration or a secondtiming configuration transmissions, the first timing configurationincluding a first time difference between a downlink communication and aresponsive uplink communication, and the second timing configurationincluding a second time difference between the downlink communicationand the responsive uplink communication, the second time differencebeing less than the first time difference, and wherein the determinationmay be based on a capability of a user equipment (UE) to transmit theresponsive uplink communication within the first time difference or thesecond time difference, and transmitting according to the first timingconfiguration or the second timing configuration based on thedetermination.

An apparatus for wireless communication is described. The apparatus mayinclude means for determining whether to use a first timingconfiguration or a second timing configuration transmissions, the firsttiming configuration including a first time difference between adownlink communication and a responsive uplink communication, and thesecond timing configuration including a second time difference betweenthe downlink communication and the responsive uplink communication, thesecond time difference being less than the first time difference, andwherein the determination may be based on a capability of a UE totransmit the responsive uplink communication within the first timedifference or the second time difference, and means for transmittingaccording to the first timing configuration or the second timingconfiguration based on the determination.

Another apparatus for wireless communication is described. The apparatusmay include a processor, memory in electronic communication with theprocessor, and instructions stored in the memory. The instructions maybe operable, when executed by the processor, to cause the apparatus todetermine whether to use a first timing configuration or a second timingconfiguration transmissions, the first timing configuration including afirst time difference between a downlink communication and a responsiveuplink communication, and the second timing configuration including asecond time difference between the downlink communication and theresponsive uplink communication, the second time difference being lessthan the first time difference, and wherein the determination may bebased on a capability of a UE to transmit the responsive uplinkcommunication within the first time difference or the second timedifference, and transmit according to the first timing configuration orthe second timing configuration based on the determination.

A non-transitory computer readable medium for wireless communication isdescribed. The non-transitory computer-readable medium may includeinstructions operable to cause a processor to determine whether to use afirst timing configuration or a second timing configurationtransmissions, the first timing configuration including a first timedifference between a downlink communication and a responsive uplinkcommunication, and the second timing configuration including a secondtime difference between the downlink communication and the responsiveuplink communication, the second time difference being less than thefirst time difference, and wherein the determination may be based on acapability of a UE to transmit the responsive uplink communicationwithin the first time difference or the second time difference, andtransmit according to the first timing configuration or the secondtiming configuration based on the determination.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the downlink communicationcontains an uplink grant and the responsive uplink communication usesresources identified in the uplink grant. In some examples of themethod, apparatus, and non-transitory computer-readable medium describedabove, the downlink communication includes downlink data and theresponsive uplink communication provides acknowledgment feedback ofsuccessful reception of the downlink data. In some examples of themethod, apparatus, and non-transitory computer-readable medium describedabove, the determination may be further based on a capability of a basestation to operate according to the first time difference or the secondtime difference.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for receiving downlink controlinformation (DCI) for the downlink communication in a common searchspace of a downlink control channel, and transmitting according to thefirst timing configuration or the second timing configuration mayinclude transmitting according to the first timing configurationresponsive to receiving the DCI for the downlink communication in thecommon search space.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for receiving DCI for the downlinkcommunication in a UE-specific search space of a downlink controlchannel, and transmitting according to the first timing configuration orthe second timing configuration comprises transmitting according to thesecond timing configuration responsive to receiving the DCI for thedownlink communication in the UE-specific search space.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for receiving DCI for the downlinkcommunication, and transmitting according to the first timingconfiguration or the second timing configuration may be further based ona format of the DCI. In some examples of the method, apparatus, andnon-transitory computer-readable medium described above, thetransmitting includes transmitting according to the first timingconfiguration for a first subset of a set of available DCI formats, andtransmitting according to the second timing configuration for a secondsubset of the set of available DCI formats.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the transmitting includesdetermining that the downlink communication includes one or more of asystem information block (SIB) transmission, a random accesstransmission, or a broadcast transmission transmitted to multiplereceivers, and transmitting according to the first timing configurationresponsive to the determining. In some examples of the method,apparatus, and non-transitory computer-readable medium described above,determining the second timing configuration includes identifying amaximum timing advance (TA) available for the responsive uplinkcommunication, and determining the second timing configuration based onthe maximum TA.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, determining the second timingconfiguration may further include processes, features, means, orinstructions for identifying a maximum transport block size (TBS)available for the responsive uplink communication, and determining thesecond timing configuration based on the maximum TA and the maximum TBS.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for receiving control informationassociated with the downlink communication in a control channel thatspans an entire subframe, and determining the first timing configurationfor the responsive uplink communication based on the receiving. Someexamples of the method, apparatus, and non-transitory computer-readablemedium described above may further include processes, features, means,or instructions for receiving control information associated with thedownlink communication in a control channel that spans a subset ofsymbols of a subframe, and determining the second timing configurationfor the responsive uplink communication based on the receiving.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for transmitting, by the UE, anindication of the capability of the UE to transmit the responsive uplinkcommunication within the first time difference or the second timedifference. Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for receiving, from the UE, anindication of the capability of the UE to transmit the responsive uplinkcommunication within the first time difference or the second timedifference.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, a maximum TBS available forthe second timing configuration is determined based on an indication ofthe capability of the UE to transmit the responsive uplink communicationwithin the first time difference or the second time difference. In someexamples of the method, apparatus, and non-transitory computer-readablemedium described above, a maximum TBS available for the second timingconfiguration may be determined based on a number of concurrenttransmissions that may be received by the UE.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for determining a third timingconfiguration that includes a third time difference between an uplinkcommunication and a responsive downlink communication, where the thirdtime difference may be less than the first time difference. Someexamples of the method, apparatus, and non-transitory computer-readablemedium described above may further include processes, features, means,or instructions for determining a third timing configuration thatincludes a third time difference between the downlink communication andthe responsive uplink communication, where the third time difference maybe less than the first time difference. In some examples of the method,apparatus, and non-transitory computer-readable medium described above,the third time difference may be less than or equal to the second timedifference.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the downlink communicationincludes an uplink grant that may be provided no earlier than a latestsubframe associated with acknowledgment receipt feedback to betransmitted using wireless resources identified in the uplink grant. Insome examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the downlink communicationincludes an uplink grant and the responsive uplink communicationincludes an uplink data message, and where the method, apparatus, andnon-transitory computer-readable medium may further include processes,features, means, or instructions for determining that the first timedifference or the second time difference jointly applies to anotherdownlink communication and another responsive uplink communication basedon the determination whether to use the first timing configuration orthe second timing configuration, where the other downlink communicationincludes a downlink grant and the other responsive uplink communicationincludes feedback responsive to the downlink grant.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for receiving radio resource control(RRC) signaling that indicates the first timing configuration or thesecond timing configuration, and determining the first timingconfiguration or the second timing configuration for each of a pluralityof transmission time intervals (TTIs) based on the RRC signaling. Someexamples of the method, apparatus, and non-transitory computer-readablemedium described above may further include processes, features, means,or instructions for dynamically determining the first timingconfiguration or the second timing configuration for each of a pluralityof transmission time intervals (TTIs). In some examples of the method,apparatus, and non-transitory computer-readable medium described above,the dynamically determining is based on one or more schedulingparameters associated with the downlink communication.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the downlink communication maybe a physical downlink shared channel (PDSCH) transmission, and theresponsive uplink communication may be a transmission of an asynchronoushybrid automatic repeat request (HARQ) feedback associated with thePDSCH transmission. In some examples of the method, apparatus, andnon-transitory computer-readable medium described above, a first numberof HARQ processes associated with the first timing configuration may begreater than a second number of HARQ processes associated with thesecond timing configuration.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for determining whether the firsttiming configuration or the second timing configuration applies forasynchronous uplink HARQ feedback based on determining whether to usethe first timing configuration or the second timing configuration fortransmissions. In some examples of the method, apparatus, andnon-transitory computer-readable medium described above, a number ofHARQ processes for the asynchronous HARQ feedback may be eight. Someexamples of the method, apparatus, and non-transitory computer-readablemedium described above may further include processes, features, means,or instructions for determining whether to use a synchronous orasynchronous uplink HARQ feedback scheme based on whether the downlinkcommunication includes a downlink grant in a common search space or aUE-specific search space.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for identifying a location of controlchannel resources for the responsive uplink communication in a downlinkcontrol channel transmission based on the second timing configurationwhere a first UE-specific offset may be associated with the first timingconfiguration and a second UE-specific offset may be associated with thesecond timing configuration. In some examples of the method, apparatus,and non-transitory computer-readable medium described above, determiningthe second timing configuration may further include processes, features,means, or instructions for identifying a periodicity for updatingchannel state information (CSI) based on the second timingconfiguration.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, identifying the periodicityfor updating CSI includes identifying one or more of a number of CSIprocesses, a CSI report type, or a reference measurement subframe. Insome examples of the method, apparatus, and non-transitorycomputer-readable medium described above, determining the second timingconfiguration may further include processes, features, means, orinstructions for determining aperiodic CSI configuration based on anumber of CSI processes supported for the second timing configuration.In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, determining the second timingconfiguration may further include processes, features, means, orinstructions for identifying a sounding reference signal (SRS) parameterbased on the second timing configuration. In some examples of themethod, apparatus, and non-transitory computer-readable medium describedabove, the SRS parameter configures aperiodic SRS transmission based thesecond timing configuration. Some examples of the method, apparatus, andnon-transitory computer-readable medium described above may furtherinclude processes, features, means, or instructions for receivingdownlink control information (DCI) for the downlink communication, andconfiguring different timing for SRS transmission and physical uplinkshared channel (PUSCH) transmission under the DCI.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the downlink communication maybe transmitted using a set of component carriers, determining the firsttiming configuration includes determining the first timing configurationfor a first subset of the set of component carriers, and determining thesecond timing configuration includes determining the second timingconfiguration for a second subset of the set of component carriers.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for determining whether each of thefirst subset of component carriers and the second subset of componentcarriers support the second timing configuration, transmitting using thesecond timing configuration for one or more of the first subset ofcomponent carriers or the second subset of component carriers when eachof the first subset of component carriers and the second subset ofcomponent carriers support the second timing configuration, andtransmitting using the first timing configuration for each componentcarrier when one or more of the first subset of component carriers orthe second subset of component carriers supports only the first timingconfiguration.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, downlink schedulinginformation for the second timing configuration may be supported in aphysical downlink control channel (PDCCH) transmission and may not besupported in an enhanced physical downlink control channel (ePDCCH)transmission. In some examples of the method, apparatus, andnon-transitory computer-readable medium described above, downlinkscheduling information for the second timing configuration may besupported in both a PDCCH transmission and an ePDCCH transmission, andavailable transport block sizes (TBSs) of the downlink schedulinginformation in the ePDCCH transmission may be different than availableTBSs in the PDCCH transmission.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the transmitting using thesecond timing configuration includes transmitting using the secondtiming configuration for the second subset of component carriers andtransmitting using the first timing configuration for the first subsetof component carriers, and the method, apparatus, and non-transitorycomputer-readable medium may further include processes, features, means,or instructions for determining that uplink control informationassociated with the first subset of component carriers and the secondsubset of component carriers is to be transmitted using a same uplinksubframe, and transmitting the uplink control information in paralleluplink control channel transmissions, multiplexing the uplink controlinformation over a same uplink control channel resource, or droppinguplink control information for one of the first subset of componentcarriers or second subset of component carriers.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for configuring one or more of CSIreporting or HARQ feedback for the first subset of the set of componentcarriers based on the first timing configuration, and configuring one ormore of CSI reporting or HARQ feedback for the second subset of the setof component carriers based on the second timing configuration.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for configuring a plurality of HARQprocesses, and where HARQ feedback for the first subset of the set ofcomponent carriers may be multiplexed with HARQ feedback for the secondsubset of the set of component carriers, HARQ feedback for the firstsubset of the set of component carriers may be transmitted using firstphysical uplink control channel (PUCCH) resources and HARQ feedback forthe second subset of the set of component carriers may be transmittedusing second PUCCH resources, and transmitting HARQ feedback for thefirst subset of the set of component carriers or the second subset ofthe set of component carriers, or both, where transmitting HARQ feedbackfor both the first subset and the second subset may be indicative of anerror case.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the downlink communication andthe responsive uplink communication may be transmitted using a timedivision duplexing (TDD) frame structure, and the method, apparatus, andnon-transitory computer-readable medium may further include processes,features, means, or instructions for identifying an uplink subframe forHARQ feedback for the first subset or the second subset of the set ofcomponent carriers, determining that a downlink subframe for at leastone component carrier of the set coincides with the uplink subframeidentified for HARQ feedback, and transmitting the HARQ feedback duringthe uplink subframe without monitoring for a downlink control messagefor the at least one component carrier during the downlink subframe.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for configuring an uplink controlchannel resource indicator based on the first timing configuration for adownlink communication TTI, determining that a second TTI may use thesecond timing configuration, and updating the uplink control channelresource indicator based on the second timing configuration for thesecond TTI.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for determining that a transmission ina first TTI may be dependent upon information in a second TTI subsequentto the first TTI, and modifying the second timing configuration toincrease the second time difference based on the determining.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the downlink communication andthe responsive uplink communication may be time division duplexing (TDD)communications, and the method, apparatus, and non-transitorycomputer-readable medium may further include processes, features, means,or instructions for determining that a first TDD downlink subframe hasthe first timing configuration, determining that a second TDD downlinksubframe has the second timing configuration, identifying a third TDDuplink subframe for transmission of HARQ feedback, and configuring HARQfeedback from the first TDD downlink subframe or the second TDD downlinksubframe, or both, to be transmitted in the third TDD uplink subframe.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, one or more of the downlinkcommunication or the responsive uplink communication may be transmittedusing a shared radio frequency spectrum band, and where the method,apparatus, and non-transitory computer-readable medium may furtherinclude processes, features, means, or instructions for modifying one ormore of a cross-transmission opportunity scheduling configuration or anumber of HARQ feedback processes based on the capability of the UE totransmit the responsive uplink communication within the first timedifference or the second time difference.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the transmitting includestransmitting an uplink grant to the UE. In some examples of the method,apparatus, and non-transitory computer-readable medium described above,the transmitting includes transmitting an uplink data transmissionresponsive to an uplink grant received from a base station.

Further scope of the applicability of the described methods andapparatuses will become apparent from the following detaileddescription, claims, and drawings. The detailed description and specificexamples are given by way of illustration only, since various changesand modifications within the spirit and scope of the description willbecome apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the following drawings. In theappended figures, similar components or features may have the samereference label. Further, various components of the same type may bedistinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If only the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

FIG. 1 illustrates an example of a system for wireless communicationthat supports latency reduction techniques in wireless communications inaccordance with aspects of the present disclosure.

FIG. 2 illustrates an example of a wireless system that supports latencyreduction in wireless communications in accordance with aspects of thepresent disclosure.

FIG. 3 illustrates an example of a frame structure that supports latencyreduction in wireless communications in accordance with aspects of thepresent disclosure.

FIG. 4A illustrates an example of a frame structure that supportslatency reduction techniques in wireless communications in accordancewith aspects of the present disclosure.

FIG. 4B illustrates an example of uplink control channel timing fordifferent component carrier timing configurations that supports latencyreduction techniques in wireless communications in accordance withaspects of the present disclosure.

FIG. 5 illustrates an example of a process flow that supports latencyreduction techniques in wireless communications in accordance withaspects of the present disclosure.

FIGS. 6 through 8 show block diagrams of a device that supports latencyreduction techniques in wireless communications in accordance withaspects of the present disclosure.

FIG. 9 illustrates a block diagram of a system including a UE thatsupports latency reduction techniques in wireless communications inaccordance with aspects of the present disclosure.

FIG. 10 illustrates a block diagram of a system including a base stationthat supports latency reduction techniques in wireless communications inaccordance with aspects of the present disclosure.

FIGS. 11 through 16 illustrate methods for latency reduction techniquesin wireless communications in accordance with aspects of the presentdisclosure.

DETAILED DESCRIPTION

A user equipment (UE) or a base station operating in a wirelesscommunications system may account for the UE's capabilities whenscheduling communications and transmitting to provide for reduced timingbetween a downlink (DL) communication and a responsive uplink (UL)communication. For example, the UE may have capabilities of operatingaccording to two or more timing configurations and resources may beallocated for transmissions based on the capability of the UE totransmit the responsive uplink communication within a first timedifference (e.g., a legacy LTE time difference), or a second timedifference (e.g., a reduced time difference relative to the legacy LTEtime difference).

By way of example, certain legacy UEs may operate with a timingconfiguration in which a downlink transmission containing a grant ofuplink resources may be transmitted in subframe n, and the responsiveuplink communication may occur at subframe n+4 or later. As used herein,legacy may refer to UEs, base stations, or other devices or componentsthat are operating according to a prior release of a wirelesscommunications standard. Such legacy UEs may operate with a timingconfiguration in which a downlink transmission containing data may betransmitted in subframe n. The UE may receive the data transmission,process the received transmission, and generate a hybrid automaticrepeat request (HARQ) acknowledgment/negative-acknowledgment (ACK/NACK)feedback to be transmitted at subframe n−4. Various aspects of thepresent disclosure provide for reduced timings between such downlinkcommunications and responsive uplink communications, which may reducelatency in the communications and enhance overall efficiency of thewireless communications system. For example, for a downlinkcommunication transmitted in subframe n, responsive uplinkcommunications may be transmitted in subframe n+3 or n+2.

In some examples, a UE or base station may be capable of operating usingtwo or more timing configurations that each include an associated timeperiod between receipt of a downlink communication and a responsiveuplink communication. In cases where a UE or base station are capable oftwo or more timing configurations, a timing configuration for atransmission may be determined and the responsive uplink communicationtransmitted according to the determined timing configuration. In caseswhere a reduced time period is used for transmissions, latency of thesystem may be reduced and the efficiency of the system enhanced.

In some cases, both a reduced time period (e.g., n+k, where k<4) and alegacy time period (e.g., n+4) may be supported by a UE, and the UE mayfallback to legacy operation in some cases where reduced timing is notfeasible or practical. In order to determine which of a reduced timeperiod timing configuration or a legacy timing configuration is to beused for a transmission, a UE may receive signaling or evaluate one ormore parameters associated with the transmission. For example, ifdownlink control information (DCI) associated with the transmission islocated in a common search space (CSS) in a physical downlink controlchannel (PDCCH) transmission, the UE may determine that the legacytiming configuration is to be used. If DCI associated with thetransmission is located in a UE-specific search space (DESS) in thePDCCH transmission, the UE may determine that the reduced time periodtiming configuration is to be used. In other examples, DCI formats maybe used to determine a timing configuration to use (e.g., DCI format 1Amay indicate a legacy timing configuration and mode-dependent DCI mayindicate a reduced time period timing configuration).

In some cases where carrier aggregation (CA) or dual-connectivity (DC)provide multiple concurrent transmissions, fallback capability to thelegacy timing configuration may be provided for a primary carrier orcell, but not one or more secondary carriers or cells. In other cases,fallback capability to the legacy timing configuration may be providedfor both primary and secondary component carriers (CCs) or cells. Insome cases, reduced time period timing configurations are provided onlyin cases where each CC is capable of supporting the reduced time period.In some examples, if reduced time period timing configurations aresupported on any of the CCs ePDCCH-based scheduling may not be supportedon any of the CCs, or may be allowed with different transport block size(TBS) limitations than PDCCH-based scheduling grants. In examples wheredifferent CCs may have different timing configurations, a same uplinksubframe may in some instances be identified for transmitting uplinkcontrol information (e.g., HARQ ACK/NACK feedback) for differentdownlink subframes. In such instances, parallel uplink control channeltransmissions may be transmitted, the control information may bemultiplexed over a same uplink control channel resource, or the uplinkcontrol channel for one of the CCs may be dropped.

In some cases, the reduced time period timing configuration may notimpact broadcast transmissions, single-carrier point-to-multipoint(SC-PTM) transmissions, or transmissions that do not have an associatedresponsive uplink transmission (e.g., system information block (SIB)related transmissions, random access related transmissions, or othertransmissions that do not have HARQ feedback).

In order to provide for reduced time period timing configurations,certain transmission parameters may be modified or have maximum valuerestrictions. For example, timing advance (TA) values may be restrictedto provide reduced propagation delay for transmissions having reducedtime period timing configurations. In some cases, a transport block size(TBS) may have a maximum size restriction to provide for processing inless time, and such size restrictions may be rank-dependentrestrictions. Timing configurations, in some cases, may be changeddynamically or changed semi-statically. In some cases, HARQ operations,physical uplink control channel (PUCCH) resource handling, channel stateinformation (CSI) handling, and/or sounding reference signal (SRS)operations may be modified based on the timing configuration for atransmission. Additionally or alternatively, time division duplexing(TDD) communications may be modified to provide downlink association setchanges and uplink scheduling changes based on different timingconfigurations. In cases that use shared radio frequency spectrum forsome or all wireless transmissions, various scheduling and HARQoperations may be determined based on different timing configurations.

Aspects of the disclosure are introduced above are described below inthe context of a wireless communications system. Subsequent figuresdepict examples of timing configurations that support latency reduction.Aspects of the disclosure are further illustrated by and described withreference to apparatus diagrams, system diagrams, and flowcharts thatrelate to latency reduction techniques in wireless communications.

FIG. 1 illustrates an example of a wireless communications system 100that supports latency reduction techniques in wireless communications inaccordance with various aspects of the present disclosure. The wirelesscommunications system 100 includes base stations 105, UEs 115, and acore network 130. In some examples, the wireless communications system100 may be a LTE (or LTE-Advanced) network. One or more of the UEs 115may have a capability for reduced time period timing configurations, andone or more of the base stations 105 may account for such capabilitieswhen scheduling communications and transmitting to provide for reducedtiming between a downlink communication and a responsive uplinkcommunication.

Base stations 105 may wirelessly communicate with UEs 115 via one ormore base station antennas. Each base station 105 may providecommunication coverage for a respective geographic coverage area 110.Communication links 125 shown in wireless communications system 100 mayinclude UL transmissions from a UE 115 to a base station 105, or DLtransmissions, from a base station 105 to a UE 115. UEs 115 may bedispersed throughout the wireless communications system 100, and each UE115 may be stationary or mobile. A UE 115 may also be referred to as amobile station, a subscriber station, a remote unit, a wireless device,an access terminal (AT), a handset, a user agent, a client, or liketerminology. A UE 115 may also be a cellular phone, a wireless modem, ahandheld device, a personal computer, a tablet, a personal electronicdevice, a machine type communication (MTC) device, etc. The UEs 115 mayhave differing capabilities, including a capability to use one orseveral timing configurations that have various time differences betweena downlink communication and a responsive uplink communication.

Base stations 105 may communicate with the core network 130 and with oneanother. For example, base stations 105 may interface with the corenetwork 130 through backhaul links 132 (e.g., S1, etc.). Base stations105 may communicate with one another over backhaul links 134 (e.g., X2,etc.) either directly or indirectly (e.g., through core network 130).Base stations 105 may perform radio configuration and scheduling forcommunication with UEs 115, or may operate under the control of a basestation controller (not shown). In some examples, base stations 105 maybe macro cells, small cells, hot spots, or the like. Base stations 105may also be referred to as eNodeBs (eNBs) 105. A base station 105 orother entity within the core network 130 may schedule communicationswith a UE 115 to account for the UE's 115 capability to transmitresponsive uplink communications within a certain time difference.

In some cases, wireless communications system 100 may utilize enhancedcomponent carriers (eCCs). An eCC may be characterized by one or morefeatures including: wider bandwidth, shorter symbol duration, shortertransmission time interval (TTIs), and modified control channelconfiguration. In some cases, an eCC may be associated with a carrieraggregation configuration or a dual connectivity configuration (e.g.,when multiple serving cells have a suboptimal or non-ideal backhaullink). An eCC may also be configured for use in unlicensed spectrum orshared spectrum (where more than one operator is allowed to use thespectrum). An eCC characterized by wide bandwidth may include one ormore segments that may be utilized by UEs 115 that are not capable ofmonitoring the whole bandwidth or prefer to use a limited bandwidth(e.g., to conserve power).

In some cases, an eCC may utilize a different symbol duration than otherCCs, which may include use of a reduced symbol duration as compared withsymbol durations of the other CCs. A shorter symbol duration isassociated with increased subcarrier spacing. In some cases, an eCC mayutilize a different symbol duration than other CCs, which may includeuse of a reduced symbol duration as compared with symbol durations ofthe other CCs. A shorter symbol duration is associated with increasedsubcarrier spacing. A device, such as a UE 115 or base station 105,utilizing eCCs may transmit wideband signals (e.g., 20, 40, 60, 80 MHz,etc.) at reduced symbol durations (e.g., 16.67 microseconds). A TTI ineCC may consist of one or multiple symbols. In some cases, the TTIduration (that is, the number of symbols in a TTI) may be variable.

HARQ may be a method of ensuring that data is received correctly over awireless communication link 125. HARQ may include a combination of errordetection (e.g., using a cyclic redundancy check (CRC)), forward errorcorrection (FEC), and retransmission (e.g., automatic repeat request(ARQ)). HARQ may improve throughput at the media access control (MAC)layer in poor radio conditions (e.g., signal-to-noise conditions). Inincremental redundancy HARQ, incorrectly received data may be stored ina buffer and combined with subsequent transmissions to improve theoverall likelihood of successfully decoding the data. In some cases,redundancy bits are added to each message prior to transmission. Thismay be useful in poor radio conditions. In other cases, redundancy bitsare not added to each transmission, but are retransmitted after thetransmitter of the original message receives a NACK indicating a failedattempt to decode the information. The chain of transmission, response,and retransmission may be referred to as a HARQ process. In some cases,a limited number of HARQ processes may be used for a given communicationlink 125. HARQ feedback may be transmitted, in some cases, in a physicalHARQ indicator channel (PHICH).

Different timing configurations may be used for HARQ feedback. Forexample, a time difference between a downlink data transmission and aresponsive uplink communication that includes an acknowledgement (ACK)or negative ACK (NACK) may vary depending on timing configuration thatis employed. The timing configuration used for communications with a UE115 may depend on the UE's 115 capability, including a capability toswitch components (e.g., within an RF chain) between uplink and downlinkmodes.

PUCCH may be used for UL ACKs, scheduling requests (SRs) and channelquality indicator (CQI), and other UL control information. A PUCCH maybe mapped to a control channel defined by a code and two consecutiveresource blocks. UL control signaling may depend on the presence oftiming synchronization for a cell. PUCCH resources for SR and CQIreporting may be assigned (and revoked) through radio resource control(RRC) signaling. In some cases, resources for SR may be assigned afteracquiring synchronization through a random access channel (RACH)procedure. In other cases, an SR may not be assigned to a UE 115 throughthe RACH (i.e., synchronized UEs may or may not have a dedicated SRchannel). PUCCH resources for SR and CQI may be lost when the UE is nolonger synchronized.

A base station 105 may gather channel condition information from a UE115 in order to efficiently configure and schedule the channel. Thisinformation may be sent from the UE 115 in the form of a channel statereport. A channel state report may contain a rank indicator (RI)requesting a number of layers to be used for DL transmissions (e.g.,based on the antenna ports of the UE 115), a precoding matrix index(PMI) indicating a preference for which precoder matrix should be used(based on the number of layers), and a channel quality indicator (CQI)representing the highest modulation and coding scheme (MCS) that may beused. CQI may be calculated by a UE 115 after receiving predeterminedpilot symbols such as a common reference signal (CRS) or CSI referencesignal (CSI-RS). RI and PMI may be excluded if the UE 115 does notsupport spatial multiplexing (or is not in support spatial mode). Thetypes of information included in the report determines a reporting type.Channel state reports may be periodic or aperiodic. That is, a basestation 105 may configure a UE 115 to send periodic reports at regularintervals, and may also request additional reports as needed. Aperiodicreports may include wideband reports indicating the channel qualityacross an entire cell bandwidth, UE selected reports indicating a subsetof the best subbands, or configured reports in which the subbandsreported are selected by the base station 105.

PDCCH carries DCI in at least one control channel element (CCE), whichmay include nine logically contiguous resource element groups (REGs),where each REG contains 4 resource elements. DCI includes informationregarding DL scheduling assignments, UL resource grants, transmissionscheme, UL power control, HARQ information, MCS and other information.The size and format of the DCI messages can differ depending on the typeand amount of information that is carried by the DCI. For example, ifspatial multiplexing is supported, the size of the DCI message is largecompared to contiguous frequency allocations. Similarly, for a systemthat employs multiple input multiple output (MIMO), the DCI must includeadditional signaling information. DCI size and format depend on theamount of information as well as factors such as bandwidth, the numberof antenna ports, and duplexing mode. PDCCH can carry DCI messagesassociated with multiple users, and each UE 115 may decode the DCImessages that are intended for it.

For example, each UE 115 may be assigned a cell radio network temporaryidentifier (C-RNTI) and CRC bits attached to each DCI may be scrambledbased on the C-RNTI. To reduce power consumption and overhead at theuser equipment, a limited set of CCE locations can be specified for DCIassociated with a specific UE 115. CCEs may be grouped (e.g., in groupsof 1, 2, 4, and 8 CCEs), and a set of CCE locations in which the userequipment may find relevant DCI may be specified. These CCEs may beknown as a search space. The search space can be partitioned into tworegions: a common CCE region or search space and a UE-specific(dedicated) CCE region or search space. The common CCE region ismonitored by all UEs served by a base station 105 and may includeinformation such as paging information, system information, randomaccess procedures, and the like. The UE-specific search space mayinclude user-specific control information. CCEs may be indexed, and thecommon search space may start from CCE 0. The starting index for a UEspecific search space depends on the C-RNTI, the subframe index, the CCEaggregation level and a random seed. A UE 115 may attempt to decode DCIby performing a process known as a blind decode, during which searchspaces are randomly decoded until the DCI is detected. During a blinddecode, the UE 115 may attempt descramble all potential DCI messagesusing its C-RNTI, and perform a CRC check to determine whether theattempt was successful.

Carriers may transmit bidirectional communications using FDD (e.g.,using paired spectrum resources) or TDD operation (e.g., using unpairedspectrum resources). Frame structures for FDD (e.g., frame structuretype 1) and TDD (e.g., frame structure type 2) may be defined. For TDDframe structures, each subframe may carry UL or DL traffic, and specialsubframes may be used to switch between DL and UL transmission.Allocation of UL and DL subframes within radio frames may be symmetricor asymmetric and may be statically determined or may be reconfiguredsemi-statically. Special subframes may carry DL or UL traffic and mayinclude a Guard Period (GP) between DL and UL traffic. Switching from ULto DL traffic may be achieved by setting a timing advance (TA) at the UE115 without the use of special subframes or a guard period. UL-DLconfigurations with switch-point periodicity equal to the frame period(e.g., 10 ms) or half of the frame period (e.g., 5 ms) may also besupported.

For example, TDD frames may include one or more special frames, and theperiod between special frames may determine the TDD DL-to-ULswitch-point periodicity for the frame. Use of TDD offers flexibledeployments without requiring paired UL-DL spectrum resources. In someTDD network deployments, interference may be caused between UL and DLcommunications (e.g., interference between UL and DL communication fromdifferent base stations, interference between UL and DL communicationsfrom base stations and UEs, etc.). For example, where different basestations 105 serve different UEs 115 within overlapping coverage areasaccording to different TDD UL-DL configurations, a UE 115 attempting toreceive and decode a DL transmission from a serving base station 105 canexperience interference from UL transmissions from other, proximatelylocated UEs 115.

A base station 105 may insert periodic pilot symbols such as CRS to aidUEs 115 in channel estimation and coherent demodulation. CRS may includeone of 504 different cell identities. They may be modulated using QPSKand power boosted (e.g., transmitted at 6 dB higher than the surroundingdata elements) to make them resilient to noise and interference. CRS maybe embedded in 4 to 24 resource elements in each resource block based onthe number of antenna ports or layers (up to 4) of the receiving UEs115. In addition to CRS, which may be utilized by all UEs 115 in thecoverage area 110 of the base station 105, demodulation reference signal(DM-RS) may be directed toward specific UEs 115 and may be transmittedonly on resource blocks assigned to those UEs 115. DM-RS may includesignals on 12 resource elements in each resource block in which they aretransmitted. The DM-RS for different antenna ports may each utilize thesame 12 resource elements, and may be distinguished using differentorthogonal cover codes (e.g., masking each signal with a differentcombination of 1 or −1 in different resource elements). In some cases,two sets of DM-RS may be transmitted in adjoining resource elements. Insome cases, additional reference signals known as channel stateinformation reference signals (CSI-RS) may be included to aid ingenerating CSI. On the UL, a UE 115 may transmit a combination ofperiodic SRS and UL DM-RS for link adaptation and demodulation,respectively.

A UE 115 may be configured to collaboratively communicate with multipleeNBs 105 through, for example, Multiple Input Multiple Output (MIMO),Coordinated Multi-Point (CoMP), or other schemes. MIMO techniques usemultiple antennas on the base stations or multiple antennas on the UE totake advantage of multipath environments to transmit multiple datastreams. CoMP includes techniques for dynamic coordination oftransmission and reception by a number of eNBs to improve overalltransmission quality for UEs as well as increasing network and spectrumutilization.

The base stations 105 of system 100 may each simultaneously supportcommunication for one or more multiple communication devices, such asUEs 115. As indicated above, and as will be discussed in more detailbelow, various examples may provide multiple different timingconfigurations for transmissions between UEs 115 and base stations 105.

FIG. 2 illustrates an example of a wireless communications system 200for latency reduction techniques in wireless communications. UE 115-amay be an example of a UE 115 as described herein with reference toFIG. 1. UE 115-a may be configured for multiple timing configurations,and may support communication on one or more component carriers (CCs)such as first CC 205 and second CC 210, which may be TDD or FDD. UE115-a also may be configured for dual connectivity communications withfirst base station 105-a and second base station 105-b via carrier 215,which may be examples of base stations 105 as described herein withreference to FIG. 1. One of the CCs, such as first CC 205 may beconfigured as a primary cell (Pcell) for UE 115-a. The first basestation 105-a may have an associated coverage area 110-a, and the secondbase station 105-b may have associated coverage area 110-b.

As indicated above, in some cases UE 115-a may be capable of multipletiming configurations. For example, the UE 115-a may have capabilitiesto receive a downlink transmission and transmit a responsive uplinkcommunication within a first time difference (e.g., a legacy LTE timedifference), or a second time difference (e.g., a reduced timedifference relative to the legacy LTE time difference). In someexamples, UE 115-a or base stations 105 may be capable of operatingusing two or more timing configurations that each include a differentassociated time period between a downlink communication and a responsiveuplink communication. In cases where a reduced time period is used fortransmissions, latency of the system may be reduced and the efficiencyof the system enhanced.

In legacy timing configurations (e.g., n+4 timing configurations),timing may be based on enhanced PDCCH (ePDCCH) control transmissions anda maximum TA value of 667 μs, corresponding to a 100 km site distancebetween a base station 105 and UE 115-a. In some examples, base stations105 may reduce the maximum site distance in order to reduce the TAassociated with transmissions to enable reduced timing configurations.For example, a reduction in the site distance from 100 km to 10 kmreduces a TA value by approximately 600 μs, and a maximum TA of 67 μsmay be established for reduced timing configurations. In ePDCCH controltransmissions, control information may span an entire subframe, whilePDCCH control transmissions may span only a subset of symbols within asubframe (e.g., four symbol or less control region size). In someexamples, reduced timing configurations may provide that DCI may betransmitted in PDCCH control transmissions, which may provide thecontrol channel transmission earlier within a subframe and provideadditional processing time. For example, with PDCCH scheduling a timesavings corresponding to 10 symbols (714 μs) for normal cyclic prefix(CP) or eight symbols (667 μs) for extended CP. Accordingly, using amaximum TA as indicated above along with PDCCH scheduling may providetime savings of approximately 1.314 ms (normal CP) or 1.267 ms (extendedCP). Such techniques may provide that a responsive uplink communicationmay be transmitted one subframe earlier, assuming 1 ms subframes, thusproviding n+3 timing.

In some cases, further timing reductions may be provided that may allowfor n+2 timing. In such cases, a maximum TBS may be provided such thatthe transport blocks associated with a downlink transmission areprocessed faster at the UE 115-a and enable n+2 reduced timing. In somecases where TBS restrictions are applied for n+3 timing, the maximumvalue for TA may be selected to provide an even subframe timing (e.g., amaximum TA of 333 μs, corresponding to a 50 km site distance, may beapplied when using TBS restrictions to provide a 1 ms time reduction foran even subframe timing). Such TA and TBS limitations may also depend onother features, such as, for example, carrier aggregation (CA), networkassisted interference cancellation (NAIC), or enhanced interferencemitigation and traffic adaptation (eIMTA) that may be present. In someexamples that use CA, multiple TA group configurations may be providedin which different UL CCs may have a maximum transmit timing differenceof about 31 μs, which may be counted into the maximum TA allowance. Forexample, in the non-CA case, a 100 μs maximum TA limitation implies amaximum 15 km site distance (100 μs*3*10⁸/2), but when operating in CAmode, the adjustment to the maximum TA limitation implies a 10.3 km sitedistance ((100 μs−31.3 μs)*3*10⁸/2).

In some cases, reduced timing configurations and legacy timingconfigurations may be semi-statically configured. In other cases,reduced timing configurations and legacy timing configurations may bedynamically configured. In some examples that provide dynamicconfiguration, DCI may be provided in a PDCCH transmission associatedwith a reduced timing configuration (e.g., n+3 or n+2 timing), and DCImay be provided in an ePDCCH transmission associated with another timing(e.g., n+4 (legacy) timing). Thus, UE 115-a may be scheduled with PDCCHin one subframe, but with ePDCCH in another subframe, and thusdynamically switched from n+4 to n+3 timing. In some examples, UE 115-amay indicate a capability of n+k timing where k<4, which may beapplicable to PDCCH only. For example, for k=3, the UE 115-a may do n+3timing for PDCCH only, and n+4 timing for both PDCCH and ePDCCH. Inexamples where k=2, the UE 115-a may do n+2 timing for PDCCH controltransmissions only, but may do n+3 or n+4 timing for PDCCH/ePDCCHcontrol transmissions.

As indicated above, in some cases TBS limitations may be provided inorder to enable reduced timing configurations. In some examples, TBSlimitations may be provided for certain timing configurations (e.g., n+3timing), and may be dependent on UE 115-a capability. In some examples,TBS restrictions may be rank-dependent, and dependent on a maximum rank(Rmax) of the UE 115-a. For example, there may be no TBS restrictiontransmissions for ranks R and lower, where R may depend on UE category(e.g., Category 2 UE, R=1; Category 5 UE, R=2). For transmissions withrank>R, restrictions may be, in some examples, a function of rank. Forexample, a restricted TBS may be provided for a rank r to provide a TBSrestriction based on a product of a maximum TBS and R/r, whereR<r<=R_(max). In some cases, parallel processing may help reduce theprocessing time for multi-layer transmissions, and thus the resultingreduction of TBS may not be linear with the number of layers. In casesthat use carrier aggregation or dual connectivity, instead of placingthe restriction on TBS on a per CC basis, restrictions may be placedjointly on the set or a subset of the configured CCs, due to the UE115-a having an overall processing limitation.

FIG. 3 illustrates an example of a frame structure 300 for latencyreduction techniques in wireless communications. Frame structure 300 maybe used for communications between UEs 115 and base stations 105 asdiscussed in FIGS. 1-2. Frame structure 300 may include downlinktransmissions 305 and uplink transmissions 310, which may make up alegacy LTE 10 ms radio frame (e.g., LTE F S1).

As indicated above, a legacy timing configuration may operate with alegacy timing in which a first downlink subframe 315 may contain adownlink transmission with a grant of uplink resources or downlink data,and the responsive uplink communication may occur at uplink subframe n+4320. In a n+3 reduced timing configuration, first downlink subframe 315may contain a downlink transmission with a grant of uplink resources ordownlink data, and the responsive uplink communication may occur atuplink subframe n+3 325. Similarly, in a n+2 reduced timingconfiguration, first downlink subframe 315 may contain a downlinktransmission with a grant of uplink resources or downlink data, and theresponsive uplink communication may occur at uplink subframe n+2 330.

While this example provides an example of downlink transmissions with anassociated responsive uplink transmission, similar timing configurationsmay be provided for uplink transmissions with an associated responsivedownlink transmission. In some cases, different timing configurationsmay be provided for uplink and downlink communications. For example, an+3 timing configuration may be used for downlink communications versusan n+2 timing configuration for uplink communications. Suchconfigurations may allow additional processing time for downlinkprocessing, which may be relatively intensive for physical downlinkshared channel (PDSCH) decoding. In some cases, uplink processing mayalso be relatively intensive, due to CSI processing and physical uplinkshared channel (PUSCH) encoding, and aperiodic CSI (A-CSI) may not beallowed to be triggered. For example, an n+2 timing configuration may beused for uplink without A-CSI triggering, and an n+3 timingconfiguration may be used for downlink communications. In otherexamples, A-CSI may be triggered but with a reference measurementsubframe earlier than the triggering subframe. In some examples, thedownlink timing gap may be configured to be no less than that for uplinkcommunications due to more intensive downlink processing. For example,possible combinations of timing may be: {DL timing, UL timing}−{n+4,n+4}, {n+4, n+3}, {n+4, n+2}, or {n+3, n+3}, {n+3, n+2}, or {n+2, n+2}.

While the example of FIG. 3 illustrates a FDD frame structure, reducedtiming configurations may also be provided for TDD frame structures.Table 1, below, depicts various TDD frame configurations, where “D”represents a downlink subframe, “U” represents an uplink subframe, and“S” represents a special subframe.

TABLE 1 depicts multiple configurations of subframes. Configuration SF 0SF 1 SF 2 SF 3 SF 4 SF 5 SF 6 SF 7 SF 8 SF 9 Configuration 0 D S U U U DS U U U Configuration 1 D S U U D D S U U D Configuration 2 D S U D D DS U D D Configuration 3 D S U U U D D D D D Configuration 4 D S U U D DD D D D Configuration 5 D S U D D D D D D D Configuration 6 D S U U U DS U U D

A UE may transmit at different times and in different subframesdepending on the frame configuration for a given transmission. Fordifferent timing configurations, downlink association sets may change,and uplink scheduling may change. The downlink HARQ association set ofan example is depicted in Table 2 for different timing configurations.In Table 2, uplink subframe n is associated with downlink subframes n-k.Thus the numbers in the top row of Table 2 are the uplink subframenumber (n), with the numbers in lower rows (k) identifying theassociated downlink subframe. This example is for TDD configuration 0.

TABLE 2 depicts DL HARQ association set for different timingconfigurations; TDD config. 0. Case SF 0 1 2 3 4 5 6 7 8 9 n + 4 — — 6 —4 — — 6 — 4 n + 3 — — — 3 3 — — — 3 3 n + 2 — — 2 2 — — — 2 2 —

In examples that have multiple possible timing configurations, and thusmultiple downlink HARQ timings, a union of downlink association sets fora timing configuration may be used, in some examples, such as depictedin Table 3, which illustrates alternative 1 for a union of associationsets for n+4 timing and n+3 timing.

TABLE 3 depicts alternative 1 of a union of DL HARQ association sets fordifferent timing configurations for TDD configuration 0. Case SF 0 1 2 34 5 6 7 8 9 n + 4 or — — 6 3 4, 3 — — 6 3 4, 3 n + 3

In other examples that have multiple possible timing configurations, aunion of downlink association sets for a timing configuration may beused but with only one valid downlink association set for an uplinksubframe, based on a scheduling decision, such as depicted in Table 4,which illustrates alternative 2 of a union of association sets for n+4timing or n+3 timing but not both.

TABLE 4 depicts alternative 2 of a union of DL HARQ association sets fordifferent timing configurations for TDD configuration 0. Case SF 0 1 2 34 5 6 7 8 9 n + 4 or n + 3 — — 6 3 4 or 3 — — 6 3 4 or 3 but not both

Tables 5 through 16 depict example downlink HARQ association sets fordifferent timing configurations for TDD configuration 1 through TDDconfiguration 6 for each alternative of unions discussed above. TDDconfiguration 1 is depicted in tables 5 and 6.

TABLE 5 depicts DL HARQ association set for different timingconfigurations for TDD configuration 1. Case SF 0 1 2 3 4 5 6 7 8 9 n +4 — — 7, 6 4 — — — 7, 6 4 — n + 3 — — 3, 6 3 — — — 3, 6 3 — n + 2 — — 3,2 2 — — — 3, 2 2 —

TABLE 6 depicts alternative 2 of a union of DL HARQ association sets fordifferent timing configurations for TDD configuration 1. Case SF 0 1 2 34 5 6 7 8 9 n + 4 or n + 3 — — {7, 6} 4 or 3 — — — {7, 6} 4 or 3 — butnot both or {3, 6} or {3, 6}

TDD configuration 2 is depicted in tables 7 and 8.

TABLE 7 depicts DL HARQ association set for different timingconfigurations for TFF configuration 2. Case SF 0 1 2 3 4 5 6 7 8 9 n +4 — — 8, 7, 4, 6 — — — — 8, 7, 4, 6 — — n + 3 — — 7, 4, 3, 6 — — — — 7,4, 3, 6 — — n + 2 — — 4, 3, 2, 6 2 — — — 4, 3, 2, 6 2 —

TABLE 8 depicts alternative 2 of a union of DL HARQ association sets fordifferent timing configurations for TDD configuration 2. Case SF 0 1 2 34 5 6 7 8 9 n + 4 or n + 3 — — {8, 7, 4, 6} — — — — {8, 7, 4, 6} — — butnot both or or {7, 4, 3, 6} {7, 4, 3, 6}

TDD configuration 3 is depicted in tables 9 and 10.

TABLE 9 depicts DL HARQ association set for different timingconfigurations for TDD configuration 3. Case SF 0 1 2 3 4 5 6 7 8 9 n +4 — — 7, 6, 11 6, 5 5, 4 — — — — — n + 3 — — 7, 6, 5 5, 4 4, 3 — — — — —n + 2 — — 7, 6, 5 5, 4 4, 3 — — — — —

TABLE 10 depicts alternative 2 of a union of DL HARQ association setsfor different timng configurations for TDD configuration 3. Case SF 0 12 3 4 5 6 7 8 9 n + 4 or n + 3 — — {7, 6, 11} {6, 5} {5, 4} — — — — —but not both or or or {7, 6, 5} {5, 4} {4, 3}

TDD configuration 4 is depicted in tables 11 and 12.

TABLE 11 depicts DL HARQ association set for different timingconfigurations for TDD configuration 4. Case SF 0 1 2 3 4 5 6 7 8 9 n +4 — — 12, 8, 7, 11 6, 5, 4, 7 — — — — — — n + 3 — — 11, 8, 7, 6 6, 5, 4,3 — — — — — — n + 2 — — 8, 7, 6, 5 6, 5, 4, 3 — — — — — —

TABLE 12 depicts alternative 2 of a union of DL HARQ association setsfor different timing configurations for TDD configuration 4. Case SF 0 12 3 4 5 6 7 8 9 n + 4 or n + — — {12, 8, 7, 11} {6, 5, 4, 7} — — — — — —3 but not or or both {11, 8, 7, 6} {6, 5, 4, 3}

TDD configuration 5 is depicted in tables 13 and 14.

TABLE 13 depicts DL HARQ association set for different timingconfigurations for TDD configuration 5. Case SF 0 1 2 3 4 5 6 7 8 9 n +4 — — 13, 12, 9, 8, 7, — — — — — — — 5, 4, 11, 6 n + 3 — — 12, 9, 8, 7,6, 5, — — — — — — — 4, 3, 11 n + 2 — — 9, 8, 7, 6, 5, 4, — — — — — — —3, 2, 11

TABLE 14 depicts alternative 2 of a union of DL HARQ association setsfor different timing configurations for TDD configuration 5. Case SF 0 12 3 4 5 6 7 8 9 n + 4 or n + — — {13, 12, 9, 8, 7, 5, 4, 11, 6} — — — —— — — 3 but not or both {12, 9, 8, 7, 6, 5, 4, 3, 11}

TDD configuration 6 is depicted in tables 15 and 16.

TABLE 15 depicts DL HARQ association set for different timingconfigurations for TDD configuration 6. Case SF 0 1 2 3 4 5 6 7 8 9 n +4 — — 7 7 5 — — 7 7 — n + 3 — — 6 4 4 — — 6 3 — n + 2 — — 3 3 3 — — 2 2—

TABLE 16 depicts alternative 2 of a union of DL HARQ association set fordifferent timing configurations for TDD configuration 6. Case SF 0 1 2 34 5 6 7 8 9 n + 4 or — — 7 or 6 7 or 4 5 or 4 — — 7 or 6 7 or 3 — n + 3but not both

In some examples, for TDD UL grant scheduling of PUSCH transmissions insubframe n, the grant may be always located in a subframe no earlierthan the last downlink subframe associated with subframe n for downlinkHARQ feedback. Such a technique may ensure downlink assignment index(DAI) in the uplink grant only needs to count already scheduled downlinksubframes, instead of counting future DL subframes.

As indicated above, in some examples timing configurations may beprovided dynamically or semi-statically. In some cases, a first UE maybe capable of doing n+4 timing only, a second UE may be capable of doingn+3 and n+4 timing, and a third UE may be capable of doing n+2, n+3, andn+4 timing. Additionally, a serving base station may be able to handlen+4 only, n+3 and n+4, n+2 and n+4, n+2, n+3 and n+4, etc. In suchexamples, a UE may be configured based on its own capability and thebase station's capability for a particular timing configuration. In someexamples, UE may be capable of n+2 timing and a base station may also becapable of n+2 timing, and the UE may be configured such that for rank 1transmissions n+2 timing is used; for rank 2 transmissions n+3 timing isused; and for rank 3 and above transmissions n+4 timing is used.Similarly, if a UE is capable of n+3 timing and the base station is alsocapable of n+3 timing, the UE may be configured such that if PDSCH/PUSCHis scheduled by PDCCH, then n+3 timing is used; and if PDSCH/PUSCH isscheduled by ePDCCH, then n+4 timing is used. Such dynamic determinationof timing may, additionally or alternatively, be based on schedulingparameters (e.g., PDCCH vs. ePDCCH, TBS size, number of layers, etc.) oran explicit indicator. In some examples, dynamic switching may bedisallowed between n+4 and n+3 timings scheduled by DCIs in UE-specificsearch space, but allowed when DCI is in the common search space, suchthat n+4 timing is scheduled for common search space DCI and n+3 timingis scheduled for UE-specific search space DCI. In some cases, a UE maybe capable of n+2 timing, but only for PDCCH scheduled traffic; and ifit is configured with n+3 or n+4, it can be scheduled by both PDCCH andePDCCH.

As indicated above, in some examples, HARQ operations may be determinedbased on one or more timing configurations used for uplink and downlinktransmissions. In some examples, asynchronous HARQ may be used fortransmission of ACK/NACK feedback. Such asynchronous HARQ may allow bothreduced timing configurations and legacy timing configurations to beavailable for PUSCH scheduling for a UE. Under asynchronous HARQ, insome examples, a retransmitted transport block may have a differenttiming configuration that the originally transmitted transport block. Insome cases, reduced timing configurations or legacy timingconfigurations may apply for asynchronous HARQ feedback based ondetermining whether to use the reduced timing configurations or thelegacy timing configurations. In some cases, a number of HARQ processesmay be kept at eight for FDD frame structures for each of the differenttiming configurations. For TDD frame structure transmissions, or fortransmissions that may use shared radio frequency spectrum, the numberof HARQ processes may be increased. In some examples, PUSCHtransmissions may be made in a special subframe, and HARQ processes maybe increased to accommodate such additional transmissions. In someexamples, HARQ processes may be configured such that synchronous HARQmay be used for transmissions scheduled via the common search space, andasynchronous HARQ may be used for transmissions scheduled via theUE-specific search space. In certain examples, the PHICH may be removedfor common search space synchronized uplink HARQ operations. In someexamples, a HARQ process ID may be included in uplink grants.

For downlink HARQ operations, the number of HARQ processes, in someexamples, may be reduced for reduced timing configurations. Soft buffermanagement may be based on the number of reduced HARQ processes, in suchcases, which may be done on a per carrier basis under CA ordual-connectivity. For example, instead of partitioning the soft bufferallocation to a CC equally to eight HARQ processes, the soft buffer maybe partitioned equally to, for example, four HARQ processes for n+2timing instead. Such soft buffer management may increase per HARQprocess soft buffer size, and hence increase the number of stored LLRs,which in some cases may benefit link level demodulation performance.

FIG. 4A illustrates an example of a frame structure 400 for latencyreduction techniques in wireless communications. Frame structure 400 maybe used for communications between UEs 115 and base stations 105 asdiscussed in FIGS. 1-2. Frame structure 400 may include downlinktransmissions 405 and uplink transmissions 410, which may make up alegacy LTE 10 ms radio frame (e.g., LTE FS1). In some cases of FS1, UEsmay be expected to receive down link assignments for the same carrierwhere HARQ-ACK may occur in the same subframe. For example, where thedownlink communication and the responsive uplink communication aretransmitted using a time division duplexing (TDD) frame structure, anuplink subframe for hybrid automatic request (HARQ) feedback for thefirst subset or the second subset of the set of component carriers maybe identified and the HARQ feedback may be transmitted during the uplinksubframe without monitoring for a downlink control message for the atleast one component carrier during the downlink subframe if a downlinksubframe for at least one component carrier of the set coincides withthe uplink subframe identified for HARQ feedback.

In the example of FIG. 4A, PUCCH resource handling may be determinedbased on one or more timing configurations used for transmissions. Forexample, for PUCCH transmissions, the associated resource in some casesdepends on the starting CCE or eCCE of the corresponding controlchannel, and for all UEs with a PUCCH in a subframe, their controlchannels may come from a same subframe. Thus, generally there is noconflict in starting CCE/eCCE values among different UEs when each UEuses a n+4 timing configuration. However, in the event that multipletiming configurations are used, conflict in starting CCE/eCCE valuesamong different UEs may be present.

For example, a first UE may be scheduled with a n+4 timing configurationin subframe n 415, which may have an associated PUCCH transmission in ULsubframe n+4 425. A second UE may be scheduled with a n+3 timingconfiguration in subframe n+1 420, which then also may have anassociated PUCCH transmission in UL subframe n+4 425. In some examples,in order to avoid a conflict, a UE-specific offset associated with eachnew timing may be used for determining a PUCCH resource for PDSCHtransmissions. Such an offset may start from the edge of the spectrum,with PUCCH resources partitioned based on different timings. In somecases, if a UE can be switched between two reduced timings, two offsetsmay be separately configured for the UE. Such a UE specific offset maybe configured at the UE via RRC signaling, for example. In some cases,both UL signals can be multiplexed over a single PUCCH resource.

In some examples, for aperiodic CSI (A-CSI), CSI processing capabilitymay be considered based on uplink scheduling timing. For example, if n+4timing is configured, a first capability may be used (e.g., only providefresh CSI updated for K1 CSI processes). If n+3 timing is configured, asecond capability may be used (e.g., only provide fresh CSI updated forK2<K1 CSI processes). If n+2 timing is configured, a third capabilitymay be used (e.g., no triggering of A-CSI). In some examples, differentrelaxations/capability for different CSI reporting types may beconfigured (e.g., wideband CSI reports vs. other CSI reports). Forexample, if wideband CSI reporting modes 1-0 and 1-1 are configured, afirst UE capability or relaxation may be used, and otherwise, if otherCSI modes are configured, a second UE capability or relaxation may beused. The reference subframe for CSI measurement may also be updated, insome examples. For example, if n+2 timing is configured, CSI may bemoved from a 4 ms gap to a 2 ms gap. In some examples, for random accessrequest (RAR) granted CSI reporting, no change may be made for the CSIreference subframe. In other examples, the reference subframe may be thesame for different timing configurations, and rules may be defined forCSI measurement subframe determination. For example, a particular set ofsubframes for measurement may be implicitly used (e.g., similar to eIMTACSI) or subframes for measurement may be based on an explicit indicationor definition of a subset of subframes for reference. For periodic CSI(P-CSI), if the reference subframe for A-CSI is changed from a min n{CQI, ref}=4 ms gap to a 3 ms (or less) gap, a same change may be madefor P-CSI, which may simplify CSI-RS/CSI-IM related configuration andresource management.

In some examples, SRS also may be triggered using different timingconfigurations. For DCI scheduling in n+4 timing configurations, and DCIscheduling in n+3 timing configurations, the SRS parameter set may bethe same or different for triggering aperiodic SRS. According to legacySRS, the SRS parameters triggered by DCI format 0 and DCI format 4 canbe separately configured. In some examples, if reduced timing is used,different SRS parameter sets may be established. For example, for DCIformat 0 using n+4 timing, a first SRS parameter set may be used, andfor DCI format 0 using n+3 timing a second SRS parameter set may beused. In some examples, the SRS symbol may be indicated as part of theSRS parameter set. In some cases, different timing for SRS transmissionand PUSCH transmission may be used under the same DCI. For example, aDCI may trigger PUSCH transmission in subframe n, but SRS transmissionin subframe n−1.

As indicated above, in some cases CA or dual connectivity may be used bya UE, and different CCs may have different timing configurations. Forexample, even if the UE is capable of doing reduced timings over allCCs, some CCs may belong to a base station or cell that is not capableof reduced timing configurations. Furthermore, in dual connectivity, thetwo groups of CCs may have different timings or the two groups may beasynchronous, and thus the maximum TA between the two groups may besignificantly different and different timing configurations may be usedbased on the various parameters. In some examples, for CCs of differenttimings, A-CSI and/or DL HARQ ACK/NACK reporting may be configured for aset of CCs based on the timing configuration for each CC. For example, afirst set of CCs may have legacy timing, while a second set of CCs mayhave reduced timing. In such cases, it may be disallowed for configuringa first CC from the first set and a second CC from the second set toform a set of CSI processes triggered by a same trigger in A-CSIreporting. That is, each set of CCs for an A-CSI trigger may have a sametiming. In some cases, if the UE is configured with CCs within a sethaving different timings, the UE may simply update a fresh CSI for theCCs whose timing is larger. For example, an A-CSI trigger may triggerCSI reporting for CC1, CC3, and CC4, where CC1 is of n+3 timing, CC3 andCC4 are of n+4 timing. If the UE receives the A-CSI trigger, the UE mayonly be required to provide fresh CSI for CC1, but not for CC3 and CC4.

In cases where different CCs may support reduced time period timingconfigurations, different timing configurations may be determined basedon capability of the different CCs. For example, unless all CCs arecapable of supporting shortened timing, reduced time period timingconfigurations may not be supported. If all of the CCs are capable ofsupporting shortened timing, reduced time period timing configurationsmay be supported for one or more of the CCs. For example, if all CCs arecapable of handling n+3 timing configurations, then both n+3 and n+4configurations may be provided. However, if one of the CCs does notsupport n+3 timing, only n+4 timing may be used over all of the CCs.

In some examples, if shortened timing is supported on any of the CCs,ePDCCH-based scheduling may not be supported on any of the CCs. In otherexamples, if shortened timing is supported on any of the CCs,ePDCCH-based scheduling may be allowed, but with different TBSlimitations on PDCCH-based and ePDCCH-based scheduling transmissions.

In some cases, if different timing configurations are supported bydifferent CCs, uplink control channel resources for the different CCsmay collide, as illustrated in FIG. 4B, which illustrates an example ofuplink control channel timing 450 for different component carrier timingconfigurations. Uplink control channel timing 450 may be used forcommunications between UEs 115 and base stations 105 as discussed inFIGS. 1-2. In this example, uplink control channel timing 450 may bebased on PDSCH transmissions 455 that may have associated uplink controlinformation to be transmitted in a PUCCH transmission 460. In theexample of FIG. 4B, a primary cell (Pcell) transmission in subframe n465 may have an n+4 timing (e.g., HARQ ACK/NACK feedback transmitted inuplink subframe n+4), while a secondary cell (Scell) transmission insubframe n+1 470 may have a reduced time period timing configuration,such as an n+3 timing (e.g., HARQ ACK/NACK feedback transmitted inuplink subframe n+3). Thus, for both the Pcell and Scell transmission,uplink control information for the different timing configurations mayhave colliding uplink transmissions to be transmitted in uplink subframen+4 475.

In such examples where different CCs may have different timingconfigurations that indicate a same uplink subframe for transmittinguplink control information (e.g., HARQ ACK/NACK feedback) for differentdownlink subframes, the colliding uplink information may be handledusing one or more techniques. In some examples, parallel uplink controlchannel transmissions may be transmitted (e.g., not a single carrierfrequency division multiplexing (SC FDM) transmission). In otherexamples, a UE may only transmit the associated PUCCH transmissionassociated with one of the CCs. For example, a UE may drop the PUCCHtransmission of a CC based on how the downlink transmission wasscheduled. For example, if a UE receives a PDCCH CSS-based grant insteadof a PDCCH UESS grant, the UE may drop the PUCCH transmission associatedwith the UESS grant. In other examples, if a UE receives a PDCCH-basedgrant instead of an ePDCCH-based grant, the UE may drop the PUCCHtransmission associated with the ePDDCH-based grant.

In some examples, the uplink control information for the different CCsmay be multiplexed (e.g., in frequency or in time) over a same PUCCHresource in subframe n+4 475. In some cases, the uplink controlinformation payload might be too large to multiplex in the same PUCCHresource, and in some examples such multiplexing may be performed whenit is determined that the uplink control information for each CC is ableto be transmitted in the same PUCCH resource. In the event that it isdetermined that the combined uplink control information for thedifferent CCs exceeds a size that may be transmitted on the PUCCHresource, parallel transmissions may be transmitted, or the uplinkcontrol information for one of the CCs may be dropped in a similarmanner as described above.

For HARQ feedback in both non-CA and CA, one PUCCH may provide feedbackfor CCs of different timings. That is, a PUCCH in subframe n may provideHARQ feedback for PDSCH transmissions in n−4 (based on 4 ms timing) andPDSCH transmissions in subframe n−3 (based on 3 ms timing). In suchcases, both HARQ transmissions may be multiplexed over a single PUCCHresource. Alternatively, each HARQ transmission may be transmitted overa PUCCH resource and two resource offsets may be specified. In otherexamples, HARQ feedback may be provided for one of the CCs (either forPDSCH in n−4 or PDSCH in n−3, but not both) or it may be treated as anerror case if both PDSCH requiring feedback in the same UL subframe aredetected. In some examples, if the PDSCH based on 4 ms timing is fromDCI in the common search space, which may be treated as a valid case.Some examples may also provide dynamic ACK/NACK resource indicator (ARI)updates, and a PUCCH resource indicator may be updated from subframe nto subframe n+1 due to scheduling of new PDSCH transmissions using a newtiming. In cases where dual connectivity is configured, there may be alook-ahead requirement, where a UE may determine how to transmit insubframe n based on information in subframe n+1. In such cases, if a UEis capable of n+2 timing under CA, only n+3 timing may be used in orderto provide for the look-ahead requirement.

In cases where shared radio frequency spectrum is used for all or aportion of wireless communications (e.g., LTE frame structure 3 (FS3) orlicense-assisted access (LAA) deployments), multiple timingconfigurations may be configured as well. In some cases, reduced timingmay impact cross-transmission opportunity (cross TxOP) management. Insome examples, if n+2 timing is configured, cross-TxOP scheduling may bedisallowed, and if n+3 timing or n+4 timing is configured, cross-TxOPscheduling may be allowed. Additionally or alternatively, if n+2 timingis configured, the maximum number of DL HARQ processes may be reducedfrom 16 to 8, and if n+3 timing or n+4 timing is configured the maximumnumber of DL HARQ processes may be maintained at 16.

FIG. 5 illustrates an example of a process flow 500 for latencyreduction techniques in wireless communications. The steps of processflow 500 may be performed by UE 115-b and base station 105-c, which maybe examples of a UE 115 and a base station 105 as described above.

The base station 105-c and UE 115-b may perform a connectionestablishment 505 to establish an RRC connection. In some examples,various configurations of parameters may be performed as part of theconnection establishment 505, such as enabling dynamic or semi-statictiming configuration changes, configuring HARQ parameters, configuringPUCCH resource offsets, CSI handling, and/or SRS handling, for example.In some cases, the UE 115-b may signal UE capability 510 to base station105-c, which may include an indication that the UE 115-b is capable ofreduced timing configurations. In some examples, UE may receive RRCsignaling that indicates a timing configuration and determine the timingconfiguration for each transmission based on the RRC signaling.

At block 515, the base station 105-c may identify the timing capabilityof the UE 115-b. Such an identification may be made based on the UE115-b indicated capability, based on a reported class of UE 115-b, orbased on some other signaling from the UE 115-b. In some examples, theUE 115-b capability 510 may be included in an information elementprovided to base station 105-c when establishing an RRC connection.

At block 520, the base station 105-c may determine a timingconfiguration for upcoming communications with the UE 115-b. Such adetermination of timing configuration may be based on a type oftransmission to be made to the UE 115-b (e.g., no reduced timing forSIB-related operations, random access related operations, broadcasttransmissions, or SC-PTM transmissions). The timing configuration forthe UE 115-b may also be determined based on TA or TBS restrictions forreduced timing configurations. Additionally or alternatively, the timingconfiguration for the UE 115-b may be determined based on a rank for thetransmission, based on the presence of multiple CCs, dual connectivity,or combinations thereof.

The base station 105-c may then transmit DCI 525 to the UE 115-b. TheDCI may include an indication of the timing configuration for aresponsive uplink transmission, in some examples. In some cases, the DCImay be transmitted in resources spanning only a portion of a subframe(e.g., PDCCH resources) or resources spanning an entire subframe (e.g.,ePDCCH resources).

At block 530, the UE 115-b may determine the timing configuration forthe transmissions. For example, the UE 115-b may determine that aresponsive uplink transmission is to be provided according to a reducedtiming configuration, according to a legacy timing configuration, orcombinations thereof. In some examples, the UE 115-b may determine thetiming configuration for the transmissions based on a type oftransmission (e.g., no reduced timing for SIB-related operations, randomaccess related operations, broadcast transmissions, or SC-PTMtransmissions). The timing configuration for the UE 115-b may also bedetermined based on TA or TBS restrictions for reduced timingconfigurations. Additionally or alternatively, the timing configurationfor the UE 115-b may be determined based on a rank for the transmission,based on the presence of multiple CCs, dual connectivity, orcombinations thereof.

The base station 105-c may then, in some examples, transmit DLcommunication 535. DL communication 535 may include an uplink grant ordownlink data, and a responsive uplink transmission may include anuplink transmission responsive to the uplink grant of ACK/NACK feedbackfor the downlink data, for example.

At block 540, the UE 115-b may perform receive processing of the DLcommunication 535 based at least in part on the determined timingconfiguration. In some examples, the receive processing may includedemodulation and decoding of the DL communication 535. In some cases,receive processing may be based on one or more parameters that aredependent upon the timing configuration, such as a number of HARQprocesses, soft buffer management, etc. The receive processing mayinclude, in some cases, determination or HARQ feedback, CSI processing,formatting of PUSCH transmissions, or combinations thereof. The UE 115-bmay then transmit the responsive UL communication 545 to the basestation 105-c.

In some examples, a downlink communication may include an uplink grantand the responsive uplink communication may include an uplink datamessage where the time difference associated with the communication mayjointly apply to another downlink communication and another responsiveuplink communication based on the determination of the timingconfiguration to use for the communication, where the other downlinktransmission may include a downlink grant and the other responsiveuplink transmission may include feedback responsive to the downlinkgrant.

FIG. 6 shows a block diagram 600 of a wireless device 605 that supportslatency reduction techniques in wireless communications in accordancewith various aspects of the present disclosure. Wireless device 605 maybe an example of aspects of a UE 115 or base station 105 as describedwith reference to FIGS. 1-2. Wireless device 605 may include receiver610, communications manager 615, and transmitter 620. Wireless device605 may also include a processor. Each of these components may be incommunication with one another (e.g., via one or more buses).

Receiver 610 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to latencyreduction techniques in wireless communications, etc.). Information maybe passed on to other components of the device. The receiver 610 may bean example of aspects of the transceiver 935 described with reference toFIG. 9.

Communications manager 615 may be an example of aspects of thecommunications manager 915 described with reference to FIG. 9.

Communications manager 615 may determine whether to use a first timingconfiguration or a second timing configuration transmissions, the firsttiming configuration including a first time difference between adownlink communication and a responsive uplink communication, and thesecond timing configuration including a second time difference betweenthe downlink communication and the responsive uplink communication, thesecond time difference being less than the first time difference, andwhere the determination is based on a capability of a UE to transmit theresponsive uplink communication within the first time difference or thesecond time difference and transmit according to the first timingconfiguration or the second timing configuration based on thedetermination.

Transmitter 620 may transmit signals generated by other components ofthe device. In some examples, the transmitter 620 may be collocated witha receiver 610 in a transceiver module. For example, the transmitter 620may be an example of aspects of the transceiver 935 described withreference to FIG. 9. The transmitter 620 may include a single antenna,or it may include a set of antennas.

FIG. 7 shows a block diagram 700 of a wireless device 705 that supportslatency reduction techniques in wireless communications in accordancewith various aspects of the present disclosure. Wireless device 705 maybe an example of aspects of a wireless device 605 or a UE 115 or basestation 105 as described with reference to FIGS. 1, 2, and 6. Wirelessdevice 705 may include receiver 710, communications manager 715, andtransmitter 720. Wireless device 705 may also include a processor. Eachof these components may be in communication with one another (e.g., viaone or more buses).

Receiver 710 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to latencyreduction techniques in wireless communications, etc.). Information maybe passed on to other components of the device. The receiver 710 may bean example of aspects of the transceiver 935 described with reference toFIG. 9.

Communications manager 715 may be an example of aspects of thecommunications manager 915 described with reference to FIG. 9.Communications manager 715 may also include timing configurationcomponent 725 and transmission configuration component 730.

Timing configuration component 725 may determine whether to use a firsttiming configuration or a second timing configuration transmissions, thefirst timing configuration including a first time difference between adownlink communication and a responsive uplink communication, and thesecond timing configuration including a second time difference betweenthe downlink communication and the responsive uplink communication, thesecond time difference being less than the first time difference. Insome examples, the determination may be based on a capability of a UE totransmit the responsive uplink communication within the first timedifference or the second time difference. The timing configurationcomponent 725, in some examples, may modify the second timingconfiguration to increase the second time difference based on the UEcapability based on the type of transmission to be transmitted, orcombinations thereof. Timing configuration component 725 may alsodetermine a third timing configuration that includes a third timedifference between the downlink communication and the responsive uplinkcommunication, where the third time difference is less than the secondtime difference. In some cases, timing configuration component 725 maydetermine the second timing configuration responsive to receiving theDCI for the downlink communication in the UE-specific search space.Timing configuration component 725 may, in some examples, dynamicallydetermine the first timing configuration or the second timingconfiguration for each of a set of transmission time intervals (TTIs).In some cases, the dynamically determining is based on one or morescheduling parameters associated with the downlink communication. Insome cases, the downlink communication is transmitted using a set ofcomponent carriers, and where the first timing configuration isdetermined for a first subset of the set of component carriers, andwhere determining the second timing configuration is determined for asecond subset of the set of component carriers.

Transmission configuration component 730 may configure a transmissionaccording to the first timing configuration or the second timingconfiguration based on the determination and, in conjunction withtransmitter 720, transmit a responsive transmission. In some cases,transmission configuration component 730 may transmit according to thefirst timing configuration responsive to receiving the DCI for thedownlink communication in the common search space, and transmitaccording to the first timing configuration or the second timingconfiguration based on a format of the DCI. In some cases, transmissionconfiguration component 730 configures an uplink data transmissionresponsive to an uplink grant received from a base station.

Transmitter 720 may transmit signals generated by other components ofthe device. In some examples, the transmitter 720 may be collocated witha receiver 710 in a transceiver module. For example, the transmitter 720may be an example of aspects of the transceiver 935 described withreference to FIG. 9. The transmitter 720 may include a single antenna,or it may include a set of antennas.

FIG. 8 shows a block diagram 800 of a communications manager 815 thatsupports latency reduction techniques in wireless communications inaccordance with various aspects of the present disclosure. Thecommunications manager 815 may be an example of aspects of acommunications manager 615, a communications manager 715, or acommunications manager 915 described with reference to FIGS. 6, 7, and9. The communications manager 815 may include timing configurationcomponent 820, transmission configuration component 825, downlink grantcomponent 830, HARQ component 835, DCI component 840, SIB component 845,TA component 850, TBS component 855, capability indication component860, uplink grant component 865, CSI component 870, SRS component 875,ARI component 880, look-ahead component 885, TDD timing configurationcomponent 890, and eCC component 895. Each of these modules maycommunicate, directly or indirectly, with one another (e.g., via one ormore buses).

Timing configuration component 820 may determine whether to use a firsttiming configuration or a second timing configuration transmissions,similarly as discussed for timing configuration component 725 of FIG. 7.In some cases, the timing configuration component 820 may dynamicallydetermining is based on one or more scheduling parameters associatedwith the downlink communication. In some cases, the downlinkcommunication is transmitted using a set of component carriers, andwhere determining the first timing configuration includes determiningthe first timing configuration for a first subset of the set ofcomponent carriers, and where determining the second timingconfiguration includes determining the second timing configuration for asecond subset of the set of component carriers. In some cases, the thirdtime difference is less than or equal to the second time difference.

Transmission configuration component 825 may transmit according to thefirst timing configuration or the second timing configuration based onthe determination, transmit according to the first timing configurationresponsive to receiving the DCI for the downlink communication in thecommon search space, and transmit according to the first timingconfiguration or the second timing configuration based on a format ofthe DCI. In some cases, the transmitting includes transmitting an uplinkdata transmission responsive to an uplink grant received from a basestation.

Downlink grant component 830 may identify the downlink communicationcontains an uplink grant and the responsive uplink communication usesresources identified in the downlink communication.

HARQ component 835 may configure reporting of HARQ feedback based on thetiming configuration, configure HARQ feedback different subsets of a setof component carriers, and multiplexed HARQ feedback for differentsubsets of the set of component carriers. In some examples, HARQcomponent 835 may configure HARQ feedback from a first TDD downlinksubframe and/or second TDD downlink subframe to be transmitted in athird TDD uplink subframe based on association rules and/or TDDconfiguration. In some cases, the downlink communication includesdownlink data and the responsive uplink communication providesacknowledgment feedback of successful reception of the downlink data. Insome cases, the downlink communication is a physical downlink sharedchannel (PDSCH) transmission, and where the responsive uplinkcommunication is a transmission of an asynchronous HARQ feedbackassociated with the PDSCH transmission. In some cases, a first number ofHARQ processes associated with the first timing configuration is greaterthan a second number of HARQ processes associated with the second timingconfiguration.

DCI component 840 may receive DCI for the downlink communication in acommon search space of a downlink control channel, receive downlinkcontrol information (DCI) for the downlink communication in aUE-specific search space of a downlink control channel, and identify alocation of the DCI. DCI component 840 may, in some examples, receivecontrol information associated with the downlink communication in acontrol channel that spans an entire subframe (e.g., ePDCCH), receivecontrol information associated with the downlink communication in acontrol channel that spans a subset of symbols of a subframe (e.g.,PDCCH), and identify a location of control channel resources for theresponsive uplink communication based on the control information. Insome cases, uplink transmissions may be transmitted according to thefirst timing configuration for a first subset of a set of available DCIformats, and may be transmitted according to the second timingconfiguration for a second subset of the set of available DCI formats.

SIB component 845 may identify one or more of a SIB transmission, arandom access transmission, or a broadcast transmission transmitted tomultiple receivers, and transmitting according to the first timingconfiguration responsive to the determining.

TA component 850 may identify a maximum timing advance (TA) availablefor the responsive uplink communication, and timing configurations maybe based on the maximum TA.

TBS component 855 may identify a maximum transport block size (TBS)available for the responsive uplink communication, and timingconfigurations may be determined based on the maximum TA and the maximumTBS. In some cases, a maximum transport block size (TBS) available forthe second timing configuration is determined based on an indication ofthe capability of the UE to transmit the responsive uplink communicationwithin the first time difference or the second time difference. In somecases, a maximum transport block size (TBS) available for the secondtiming configuration is determined based on a number of concurrenttransmissions that may be received by the UE.

Capability indication component 860 in cases where communicationsmanager 815 is part of a UE, may provide an indication of the capabilityof the UE to transmit the responsive uplink communication within thefirst time difference or the second time difference. Capabilityindication component 860 in cases where communications manager 815 ispart of a base station, may receive, from the UE, an indication of thecapability of the UE to transmit the responsive uplink communicationwithin the first time difference or the second time difference.

Uplink grant component 865 may identify that the downlink communicationincludes an uplink grant that is provided no earlier than a latestsubframe associated with acknowledgment receipt feedback to betransmitted using wireless resources identified in the uplink grant. Insome cases, the transmitting includes transmitting an uplink grant tothe UE.

CSI component 870 may determine that the second timing configurationfurther includes identifying a periodicity for updating CSI based on theidentified second timing configuration and identify the periodicity forupdating CSI includes identifying one or more of a number of CSIprocesses, a CSI report type, or a reference measurement subframe.

SRS component 875 may determine the second timing configuration based onidentifying a SRS parameter based on the identified second timingconfiguration.

ARI component 880 may configure an uplink control channel resourceindicator based on the first timing configuration for a downlinkcommunication time interval (TTI) and update the uplink control channelresource indicator based on the second timing configuration for thesecond TTI.

Look-ahead component 885 may determine that a transmission in a firsttime interval (TTI) is dependent upon information in a second TTIsubsequent to the first TTI.

TDD timing configuration component 890 may determine TDD timingconfigurations, and HARQ associations.

ECC component 895 may manage communications using shared radio frequencyspectrum. In some cases, one or more of the downlink communication orthe responsive uplink communication are transmitted using a shared radiofrequency spectrum band, and the ECC component may modify one or more ofa cross-transmission opportunity scheduling configuration or a number ofHARQ feedback processes based on the capability of the UE to transmitthe responsive uplink communication within the first time difference orthe second time difference.

FIG. 9 shows a diagram of a system 900 including a device 905 thatsupports latency reduction techniques in wireless communications inaccordance with various aspects of the present disclosure. Device 905may be an example of or include the components of wireless device 605,wireless device 705, or a UE 115 as described above, e.g., withreference to FIGS. 1, 6, and 7. Device 905 may include components forbi-directional voice and data communications including components fortransmitting and receiving communications, including UE communicationsmanager 915, processor 920, memory 925, software 930, transceiver 935,antenna 940, and I/O controller 945.

Processor 920 may include an intelligent hardware device, (e.g., ageneral-purpose processor, a digital signal processor (DSP), a centralprocessing unit (CPU), a microcontroller, an application specificintegrated circuit (ASIC), a field-programmable gate array (FPGA), aprogrammable logic device, a discrete gate or transistor logiccomponent, a discrete hardware component, or any combination thereof).In some cases, processor 920 may be configured to operate a memory arrayusing a memory controller. In other cases, a memory controller may beintegrated into processor 920. Processor 920 may be configured toexecute computer-readable instructions stored in a memory to performvarious functions (e.g., functions or tasks supporting latency reductiontechniques in wireless communications).

Memory 925 may include random access memory (RAM) and read only memory(ROM). The memory 925 may store computer-readable, computer-executablesoftware 930 including instructions that, when executed, cause theprocessor to perform various functions described herein. In some cases,the memory 925 may contain, among other things, a Basic Input-Outputsystem (BIOS) which may control basic hardware and/or software operationsuch as the interaction with peripheral components or devices.

Software 930 may include code to implement aspects of the presentdisclosure, including code to support latency reduction techniques inwireless communications. Software 930 may be stored in a non-transitorycomputer-readable medium such as system memory or other memory. In somecases, the software 930 may not be directly executable by the processorbut may cause a computer (e.g., when compiled and executed) to performfunctions described herein.

Transceiver 935 may communicate bi-directionally, via one or moreantennas, wired, or wireless links as described above. For example, thetransceiver 935 may represent a wireless transceiver and may communicatebi-directionally with another wireless transceiver. The transceiver 935may also include a modem to modulate the packets and provide themodulated packets to the antennas for transmission, and to demodulatepackets received from the antennas.

In some cases, the wireless device may include a single antenna 940.However, in some cases the device may have more than one antenna 940,which may be capable of concurrently transmitting or receiving multiplewireless transmissions.

I/O controller 945 may manage input and output signals for device 905.I/O controller 945 may also manage peripherals not integrated intodevice 905. In some cases, I/O controller 945 may represent a physicalconnection or port to an external peripheral. In some cases, I/Ocontroller 945 may utilize an operating system such as iOS®, ANDROID®,MS-DOS®, MS-WINDOWS®, OS/2®, UNIX®, LINUX®, or another known operatingsystem.

FIG. 10 shows a diagram of a system 1000 including a device 1005 thatsupports latency reduction techniques in wireless communications inaccordance with various aspects of the present disclosure. Device 1005may be an example of or include the components of wireless device 705,wireless device 805, or a base station 105 as described above, e.g.,with reference to FIGS. 1, 7, and 8. Device 1005 may include componentsfor bi-directional voice and data communications including componentsfor transmitting and receiving communications, including base stationcommunications manager 1015, processor 1020, memory 1025, software 1030,transceiver 1035, antenna 1040, network communications manager 1045, andinter-NodeB communications manager 1050.

Base station communications manager 1015 may be an example of aspects ofa communications manager 615 or a communications manager 715 describedwith reference to FIGS. 6 and 7.

Processor 1020 may include an intelligent hardware device, (e.g., ageneral-purpose processor, a digital signal processor (DSP), a centralprocessing unit (CPU), a microcontroller, an application specificintegrated circuit (ASIC), a field-programmable gate array (FPGA), aprogrammable logic device, a discrete gate or transistor logiccomponent, a discrete hardware component, or any combination thereof).In some cases, processor 1020 may be configured to operate a memoryarray using a memory controller. In other cases, a memory controller maybe integrated into processor 1020. Processor 1020 may be configured toexecute computer-readable instructions stored in a memory to performvarious functions (e.g., functions or tasks supporting latency reductiontechniques in wireless communications).

Memory 1025 may include random access memory (RAM) and read only memory(ROM). The memory 1025 may store computer-readable, computer-executablesoftware 1030 including instructions that, when executed, cause theprocessor to perform various functions described herein. In some cases,the memory 1025 may contain, among other things, a Basic Input-Outputsystem (BIOS) which may control basic hardware and/or software operationsuch as the interaction with peripheral components or devices.

Software 1030 may include code to implement aspects of the presentdisclosure, including code to support latency reduction techniques inwireless communications. Software 1030 may be stored in a non-transitorycomputer-readable medium such as system memory or other memory. In somecases, the software 1030 may not be directly executable by the processorbut may cause a computer (e.g., when compiled and executed) to performfunctions described herein.

Transceiver 1035 may communicate bi-directionally, via one or moreantennas, wired, or wireless links as described above. For example, thetransceiver 1035 may represent a wireless transceiver and maycommunicate bi-directionally with another wireless transceiver. Thetransceiver 1035 may also include a modem to modulate the packets andprovide the modulated packets to the antennas for transmission, and todemodulate packets received from the antennas.

In some cases, the wireless device may include a single antenna 1040.However, in some cases the device may have more than one antenna 1040,which may be capable of concurrently transmitting or receiving multiplewireless transmissions.

Network communications manager 1045 may manage communications with thecore network (e.g., via one or more wired backhaul links). For example,the network communications manager 1045 may manage the transfer of datacommunications for client devices, such as one or more UEs 115.

Inter-NodeB communications manager 1050 may manage communications withother base station 105, and may include a controller or scheduler forcontrolling communications with UEs 115 in cooperation with other basestations 105. For example, the inter-NodeB communications manager 1050may coordinate scheduling for transmissions to UEs 115 for variousinterference mitigation techniques such as beamforming or jointtransmission. In some examples, inter-NodeB communications manager 1050may provide an X2 interface within an LTE/LTE-A wireless communicationnetwork technology to provide communication between base stations 105.

FIG. 11 shows a flowchart illustrating a method 1100 for latencyreduction techniques in wireless communications in accordance withvarious aspects of the present disclosure. The operations of method 1100may be implemented by a UE 115 or base station 105 or its components asdescribed herein. For example, the operations of method 1100 may beperformed by a communications manager as described with reference toFIGS. 6 through 8. In some examples, a UE 115 or base station 105 mayexecute a set of codes to control the functional elements of the deviceto perform the functions described below. Additionally or alternatively,the UE 115 or base station 105 may perform aspects the functionsdescribed below using special-purpose hardware.

At block 1105 the UE 115 or base station 105 may determine whether touse a first timing configuration or a second timing configuration fortransmissions. The first timing configuration may include a first timedifference between a downlink communication and a responsive uplinkcommunication, and the second timing configuration include a second timedifference between the downlink communication and the responsive uplinkcommunication, the second time difference being less than the first timedifference. The determination may be based at least in part on acapability of a user equipment (UE) to transmit the responsive uplinkcommunication within the first time difference or the second timedifference. The operations of block 1105 may be performed according tothe methods described with reference to FIGS. 1 through 5. In certainexamples, aspects of the operations of block 1105 may be performed by atiming configuration component as described with reference to FIGS. 6through 8.

At block 1110 the UE 115 or base station 105 may transmit according tothe first timing configuration or the second timing configuration basedon the determination. The operations of block 1110 may be performedaccording to the methods described with reference to FIGS. 1 through 5.In certain examples, aspects of the operations of block 1110 may beperformed by a transmission configuration component as described withreference to FIGS. 6 through 8, which may operate in cooperation with atransmitter 620 or 720 as described with reference to FIG. 6 or 7, orantenna(s) 940 and transceiver(s) 935 as described with reference toFIG. 9, or antenna(s) 1040 and transceiver(s) 1035 as described withreference to FIG. 10.

FIG. 12 shows a flowchart illustrating a method 1200 for latencyreduction techniques in wireless communications in accordance withvarious aspects of the present disclosure. The operations of method 1200may be implemented by a UE 115 or base station 105 or its components asdescribed herein. For example, the operations of method 1200 may beperformed by a communications manager as described with reference toFIGS. 6 through 8. In some examples, a UE 115 or base station 105 mayexecute a set of codes to control the functional elements of the deviceto perform the functions described below. Additionally or alternatively,the UE 115 or base station 105 may perform aspects the functionsdescribed below using special-purpose hardware. In some examples, adownlink communication may include an uplink grant and the responsiveuplink communication may include an uplink data message where the timedifference associated with the communication may jointly apply toanother downlink communication and another responsive uplinkcommunication based on the determination of the timing configuration touse for the communication, where the other downlink transmission mayinclude a downlink grant and the other responsive uplink transmissionmay include feedback responsive to the downlink grant.

At block 1205 the UE 115 or base station 105 may receive downlinkcontrol information (DCI) for a downlink communication in a commonsearch space of a downlink control channel. The operations of block 1205may be performed according to the methods described with reference toFIGS. 1 through 5. In certain examples, aspects of the operations ofblock 1205 may be performed by a DCI component as described withreference to FIGS. 6 through 8, which may operate in cooperation with areceiver 610 or 710 as described with reference to FIG. 6 or 7, orantenna(s) 940 and transceiver(s) 935 as described with reference toFIG. 9, or antenna(s) 1040 and transceiver(s) 1035 as described withreference to FIG. 10.

At block 1210 the UE 115 or base station 105 may transmit according tothe first timing configuration responsive to receiving the DCI for thedownlink communication in the common search space. The operations ofblock 1210 may be performed according to the methods described withreference to FIGS. 1 through 5. In certain examples, aspects of theoperations of block 1210 may be performed by a transmissionconfiguration component as described with reference to FIGS. 6 through8, which may operate in cooperation with a transmitter 620 or 720 asdescribed with reference to FIG. 6 or 7, or antenna(s) 940 andtransceiver(s) 935 as described with reference to FIG. 9, or antenna(s)1040 and transceiver(s) 1035 as described with reference to FIG. 10.

At block 1215 the UE 115 or base station 105 may receive downlinkcontrol information (DCI) for a downlink communication in a UE-specificsearch space of a downlink control channel. The operations of block 1215may be performed according to the methods described with reference toFIGS. 1 through 5. In certain examples, aspects of the operations ofblock 1215 may be performed by a DCI component as described withreference to FIGS. 6 through 8, which may operate in cooperation with areceiver 610 or 710 as described with reference to FIG. 6 or 7, orantenna(s) 940 and transceiver(s) 935 as described with reference toFIG. 9, or antenna(s) 1040 and transceiver(s) 1035 as described withreference to FIG. 10.

At block 1220 the UE 115 or base station 105 may transmit according tothe second timing configuration responsive to receiving the DCI for thedownlink communication in the UE-specific search space. The operationsof block 1220 may be performed according to the methods described withreference to FIGS. 1 through 5. In certain examples, aspects of theoperations of block 1220 may be performed by a timing configurationcomponent as described with reference to FIGS. 6 through 8, which mayoperate in cooperation with a transmitter 620 or 720 as described withreference to FIG. 6 or 7, or antenna(s) 940 and transceiver(s) 935 asdescribed with reference to FIG. 9, or antenna(s) 1040 andtransceiver(s) 1035 as described with reference to FIG. 10.

FIG. 13 shows a flowchart illustrating a method 1300 for latencyreduction techniques in wireless communications in accordance withvarious aspects of the present disclosure. The operations of method 1300may be implemented by a UE 115 or base station 105 or its components asdescribed herein. For example, the operations of method 1300 may beperformed by a communications manager as described with reference toFIGS. 6 through 8. In some examples, a UE 115 or base station 105 mayexecute a set of codes to control the functional elements of the deviceto perform the functions described below. Additionally or alternatively,the UE 115 or base station 105 may perform aspects the functionsdescribed below using special-purpose hardware.

At block 1305 the UE 115 or base station 105 may determine the secondtiming configuration comprises identifying a maximum timing advance (TA)available for the responsive uplink communication. The operations ofblock 1305 may be performed according to the methods described withreference to FIGS. 1 through 5. In certain examples, aspects of theoperations of block 1305 may be performed by a TA component as describedwith reference to FIGS. 6 through 8.

At block 1310 the UE 115 or base station 105 may identify a maximumtransport block size (TBS) available for the responsive uplinkcommunication, and determine the second timing configuration based atleast in part on the maximum TA and the maximum TBS. The operations ofblock 1310 may be performed according to the methods described withreference to FIGS. 1 through 5. In certain examples, aspects of theoperations of block 1310 may be performed by a TBS component asdescribed with reference to FIGS. 6 through 8.

FIG. 14 shows a flowchart illustrating a method 1400 for latencyreduction techniques in wireless communications in accordance withvarious aspects of the present disclosure. The operations of method 1400may be implemented by a UE 115 or base station 105 or its components asdescribed herein. For example, the operations of method 1400 may beperformed by a communications manager as described with reference toFIGS. 6 through 8. In some examples, a UE 115 or base station 105 mayexecute a set of codes to control the functional elements of the deviceto perform the functions described below. Additionally or alternatively,the UE 115 or base station 105 may perform aspects the functionsdescribed below using special-purpose hardware.

At block 1405 the UE 115 or base station 105 may receive controlinformation associated with the downlink communication in a controlchannel that spans an entire subframe. The operations of block 1405 maybe performed according to the methods described with reference to FIGS.1 through 5. In certain examples, aspects of the operations of block1405 may be performed by a DCI component as described with reference toFIGS. 6 through 8, which may operate in cooperation with a receiver 610or 710 as described with reference to FIG. 6 or 7, or antenna(s) 940 andtransceiver(s) 935 as described with reference to FIG. 9, or antenna(s)1040 and transceiver(s) 1035 as described with reference to FIG. 10.

At block 1410 the UE 115 or base station 105 may determine the firsttiming configuration for the responsive uplink communication based atleast in part on the receiving. The operations of block 1410 may beperformed according to the methods described with reference to FIGS. 1through 5. In certain examples, aspects of the operations of block 1410may be performed by a timing configuration component as described withreference to FIGS. 6 through 8.

At block 1415 the UE 115 or base station 105 may receive controlinformation associated with the downlink communication in a controlchannel that spans a subset of symbols of a subframe. The operations ofblock 1415 may be performed according to the methods described withreference to FIGS. 1 through 5. In certain examples, aspects of theoperations of block 1415 may be performed by a DCI component asdescribed with reference to FIGS. 6 through 8, which may operate incooperation with a receiver 610 or 710 as described with reference toFIG. 6 or 7, or antenna(s) 940 and transceiver(s) 935 as described withreference to FIG. 9, or antenna(s) 1040 and transceiver(s) 1035 asdescribed with reference to FIG. 10.

At block 1420 the UE 115 or base station 105 may determine the secondtiming configuration for the responsive uplink communication based atleast in part on the receiving. The operations of block 1420 may beperformed according to the methods described with reference to FIGS. 1through 5. In certain examples, aspects of the operations of block 1420may be performed by a timing configuration component as described withreference to FIGS. 6 through 8.

FIG. 15 shows a flowchart illustrating a method 1500 for latencyreduction techniques in wireless communications in accordance withvarious aspects of the present disclosure. The operations of method 1500may be implemented by a base station 105 or its components as describedherein. For example, the operations of method 1500 may be performed by acommunications manager as described with reference to FIGS. 6 through 8.In some examples, base station 105 may execute a set of codes to controlthe functional elements of the device to perform the functions describedbelow. Additionally or alternatively, the base station 105 may performaspects the functions described below using special-purpose hardware. Insome examples, UE may receive RRC signaling that indicates a timingconfiguration and determine the timing configuration for eachtransmission based on the RRC signaling.

At block 1505 the base station 105 may receive, from the UE, anindication of the capability of the UE to transmit the responsive uplinkcommunication within the first time difference or the second timedifference. The operations of block 1505 may be performed according tothe methods described with reference to FIGS. 1 through 5. In certainexamples, aspects of the operations of block 1505 may be performed by acapability indication component as described with reference to FIGS. 6through 8, which may operate in cooperation with a receiver 610 or 710as described with reference to FIG. 6 or 7, or antenna(s) 940 andtransceiver(s) 935 as described with reference to FIG. 9, or antenna(s)1040 and transceiver(s) 1035 as described with reference to FIG. 10.

At block 1510 the base station 105 may dynamically determine the firsttiming configuration or the second timing configuration for each of aplurality of transmission time intervals (TTIs). The operations of block1510 may be performed according to the methods described with referenceto FIGS. 1 through 5. In certain examples, aspects of the operations ofblock 1510 may be performed by a timing configuration component asdescribed with reference to FIGS. 6 through 8.

FIG. 16 shows a flowchart illustrating a method 1600 for latencyreduction techniques in wireless communications in accordance withvarious aspects of the present disclosure. The operations of method 1600may be implemented by a UE 115 or base station 105 or its components asdescribed herein. For example, the operations of method 1600 may beperformed by a communications manager as described with reference toFIGS. 6 through 8. In some examples, a UE 115 or base station 105 mayexecute a set of codes to control the functional elements of the deviceto perform the functions described below. Additionally or alternatively,the UE 115 or base station 105 may perform aspects the functionsdescribed below using special-purpose hardware.

At block 1605 the UE 115 or base station 105 may determine that a TDDdownlink subframe has the second timing configuration. The operations ofblock 1605 may be performed according to the methods described withreference to FIGS. 1 through 5. In certain examples, aspects of theoperations of block 1605 may be performed by a TDD timing configurationcomponent as described with reference to FIGS. 6 through 8.

At block 1610 the UE 115 or base station 105 may identify a TDD uplinksubframe for transmission of hybrid automatic repeat request (HARQ)feedback. The operations of block 1610 may be performed according to themethods described with reference to FIGS. 1 through 5. In certainexamples, aspects of the operations of block 1610 may be performed by aHARQ component as described with reference to FIGS. 6 through 8.

At block 1615 the UE 115 or base station 105 may configure HARQ feedbackfrom a first TDD downlink subframe and/or a second TDD downlink subframeto be transmitted in a third TDD uplink subframe. The operations ofblock 1615 may be performed according to the methods described withreference to FIGS. 1 through 5. In certain examples, aspects of theoperations of block 1615 may be performed by a HARQ component asdescribed with reference to FIGS. 6 through 8.

It should be noted that the methods described above describe possibleimplementations, and that the operations and the steps may be rearrangedor otherwise modified and that other implementations are possible.Furthermore, aspects from two or more of the methods may be combined.

Techniques described herein may be used for various wirelesscommunications systems such as code division multiple access (CDMA),time division multiple access (TDMA), frequency division multiple access(FDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), and other systems.The terms “system” and “network” are often used interchangeably. A codedivision multiple access (CDMA) system may implement a radio technologysuch as CDMA2000, Universal Terrestrial Radio Access (UTRA), etc.CDMA2000 covers IS-2000, IS-95, and IS-856 standards. IS-2000 Releasesmay be commonly referred to as CDMA2000 1×, 1×, etc. IS-856 (TIA-856) iscommonly referred to as CDMA2000 1×V-DO, High Rate Packet Data (HRPD),etc. UTRA includes Wideband CDMA (WCDMA) and other variants of CDMA. Atime division multiple access (TDMA) system may implement a radiotechnology such as Global System for Mobile Communications (GSM).

An orthogonal frequency division multiple access (OFDMA) system mayimplement a radio technology such as Ultra Mobile Broadband (UMB),Evolved UTRA (E-UTRA), Institute of Electrical and Electronics Engineers(IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM,etc. UTRA and E-UTRA are part of Universal Mobile Telecommunicationssystem (UMTS). 3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A)are new releases of Universal Mobile Telecommunications System (UMTS)that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A, and Global System forMobile communications (GSM) are described in documents from theorganization named “3rd Generation Partnership Project” (3GPP). CDMA2000and UMB are described in documents from an organization named “3rdGeneration Partnership Project 2” (3GPP2). The techniques describedherein may be used for the systems and radio technologies mentionedabove as well as other systems and radio technologies. While aspects anLTE system may be described for purposes of example, and LTE terminologymay be used in much of the description, the techniques described hereinare applicable beyond LTE applications.

In LTE/LTE-A networks, including such networks described herein, theterm evolved node B (eNB) may be generally used to describe the basestations. The wireless communications system or systems described hereinmay include a heterogeneous LTE/LTE-A network in which different typesof evolved node B (eNBs) provide coverage for various geographicalregions. For example, each eNB or base station may provide communicationcoverage for a macro cell, a small cell, or other types of cell. Theterm “cell” may be used to describe a base station, a carrier orcomponent carrier associated with a base station, or a coverage area(e.g., sector, etc.) of a carrier or base station, depending on context.

Base stations may include or may be referred to by those skilled in theart as a base transceiver station, a radio base station, an accesspoint, a radio transceiver, a NodeB, eNodeB (eNB), Home NodeB, a HomeeNodeB, or some other suitable terminology. The geographic coverage areafor a base station may be divided into sectors making up only a portionof the coverage area. The wireless communications system or systemsdescribed herein may include base stations of different types (e.g.,macro or small cell base stations). The UEs described herein may be ableto communicate with various types of base stations and network equipmentincluding macro eNBs, small cell eNBs, relay base stations, and thelike. There may be overlapping geographic coverage areas for differenttechnologies.

A macro cell generally covers a relatively large geographic area (e.g.,several kilometers in radius) and may allow unrestricted access by UEswith service subscriptions with the network provider. A small cell is alower-powered base station, as compared with a macro cell, that mayoperate in the same or different (e.g., licensed, unlicensed, etc.)frequency bands as macro cells. Small cells may include pico cells,femto cells, and micro cells according to various examples. A pico cell,for example, may cover a small geographic area and may allowunrestricted access by UEs with service subscriptions with the networkprovider. A femto cell may also cover a small geographic area (e.g., ahome) and may provide restricted access by UEs having an associationwith the femto cell (e.g., UEs in a closed subscriber group (CSG), UEsfor users in the home, and the like). An eNB for a macro cell may bereferred to as a macro eNB. An eNB for a small cell may be referred toas a small cell eNB, a pico eNB, a femto eNB, or a home eNB. An eNB maysupport one or multiple (e.g., two, three, four, and the like) cells(e.g., component carriers). A UE may be able to communicate with varioustypes of base stations and network equipment including macro eNBs, smallcell eNBs, relay base stations, and the like.

The wireless communications system or systems described herein maysupport synchronous or asynchronous operation. For synchronousoperation, the base stations may have similar frame timing, andtransmissions from different base stations may be approximately alignedin time. For asynchronous operation, the base stations may havedifferent frame timing, and transmissions from different base stationsmay not be aligned in time. The techniques described herein may be usedfor either synchronous or asynchronous operations.

The downlink transmissions described herein may also be called forwardlink transmissions while the uplink transmissions may also be calledreverse link transmissions. Each communication link describedherein—including, for example, wireless communications system 100 and200 of FIGS. 1 and 2—may include one or more carriers, where eachcarrier may be a signal made up of multiple sub-carriers (e.g., waveformsignals of different frequencies).

The description set forth herein, in connection with the appendeddrawings, describes example configurations and does not represent allthe examples that may be implemented or that are within the scope of theclaims. The term “exemplary” used herein means “serving as an example,instance, or illustration,” and not “preferred” or “advantageous overother examples.” The detailed description includes specific details forthe purpose of providing an understanding of the described techniques.These techniques, however, may be practiced without these specificdetails. In some instances, well-known structures and devices are shownin block diagram form in order to avoid obscuring the concepts of thedescribed examples.

Information and signals described herein may be represented using any ofa variety of different technologies and techniques. For example, data,instructions, commands, information, signals, bits, symbols, and chipsthat may be referenced throughout the above description may berepresented by voltages, currents, electromagnetic waves, magneticfields or particles, optical fields or particles, or any combinationthereof.

The various illustrative blocks and modules described in connection withthe disclosure herein may be implemented or performed with ageneral-purpose processor, a digital signal processor (DSP), anapplication-specific integrated circuit (ASIC), a field-programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices (e.g., a combinationof a DSP and a microprocessor, multiple microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration).

The functions described herein may be implemented in hardware, softwareexecuted by a processor, firmware, or any combination thereof. Ifimplemented in software executed by a processor, the functions may bestored on or transmitted over as one or more instructions or code on acomputer-readable medium. Other examples and implementations are withinthe scope of the disclosure and appended claims. For example, due to thenature of software, functions described above can be implemented usingsoftware executed by a processor, hardware, firmware, hardwiring, orcombinations of any of these. Features implementing functions may alsobe physically located at various positions, including being distributedsuch that portions of functions are implemented at different physicallocations. Also, as used herein, including in the claims, “or” as usedin a list of items (for example, a list of items prefaced by a phrasesuch as “at least one of” or “one or more of”) indicates an inclusivelist such that, for example, a list of at least one of A, B, or C meansA or B or C or AB or AC or BC or ABC (i.e., A and B and C).

All structural and functional equivalents to the elements of the variousaspects described throughout this disclosure that are known or latercome to be known to those of ordinary skill in the art are expresslyincorporated herein by reference and are intended to be encompassed bythe claims. Moreover, nothing disclosed herein is intended to bededicated to the public regardless of whether such disclosure isexplicitly recited in the claims. The words “module,” “mechanism,”“element,” “device,” “component,” and the like may not be a substitutefor the word “means.” As such, no claim element is to be construed as ameans plus function unless the element is expressly recited using thephrase “means for.”

Computer-readable media includes both non-transitory computer storagemedia and communication media including any medium that facilitatestransfer of a computer program from one place to another. Anon-transitory storage medium may be any available medium that can beaccessed by a general purpose or special purpose computer. By way ofexample, and not limitation, non-transitory computer-readable media maycomprise RAM, ROM, electrically erasable programmable read only memory(EEPROM), compact disk (CD) ROM or other optical disk storage, magneticdisk storage or other magnetic storage devices, or any othernon-transitory medium that can be used to carry or store desired programcode means in the form of instructions or data structures and that canbe accessed by a general-purpose or special-purpose computer, or ageneral-purpose or special-purpose processor. Also, any connection isproperly termed a computer-readable medium. For example, if the softwareis transmitted from a website, server, or other remote source using acoaxial cable, fiber optic cable, twisted pair, digital subscriber line(DSL), or wireless technologies such as infrared, radio, and microwave,then the coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave are included in the definition of medium. Disk and disc,as used herein, include CD, laser disc, optical disc, digital versatiledisc (DVD), floppy disk and Blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above are also included within the scope ofcomputer-readable media.

The description herein is provided to enable a person skilled in the artto make or use the disclosure. Various modifications to the disclosurewill be readily apparent to those skilled in the art, and the genericprinciples defined herein may be applied to other variations withoutdeparting from the scope of the disclosure. Thus, the disclosure is notlimited to the examples and designs described herein, but is to beaccorded the broadest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A method for wireless communication, performed bya user equipment (UE), comprising: determining, based on a capability ofthe UE, whether to use a first timing configuration or a second timingconfiguration for transmissions, the first timing configurationincluding a first time difference between a downlink communication and aresponsive uplink communication, the downlink communication being aphysical downlink shared channel (PDSCH) transmission, the responsiveuplink communication being a physical uplink control channel (PUCCH)transmission, and the second timing configuration including a secondtime difference between the downlink communication and the responsiveuplink communication, the second time difference being less than thefirst time difference; and transmitting the responsive uplinkcommunication to a base station according to either the first timingconfiguration or the second timing configuration based on thedetermination.
 2. The method of claim 1, wherein the downlinkcommunication includes downlink data and the responsive uplinkcommunication provides acknowledgment feedback of successful receptionof the downlink data.
 3. The method of claim 1, further comprising:receiving downlink control information (DCI) for the downlinkcommunication; and wherein transmitting according to the first timingconfiguration or the second timing configuration is further based atleast in part on a format of the DCI.
 4. The method of claim 3, whereinthe transmitting comprises: transmitting according to the first timingconfiguration for a first subset of a set of available DCI formats; andtransmitting according to the third timing configuration for a secondsubset of the set of available DCI formats.
 5. The method of claim 1,wherein determining whether to use the first timing configuration or thesecond timing configuration comprises: identifying a maximum timingadvance (TA) available for the responsive uplink communication; anddetermining to use either the first timing configuration or the secondtiming configuration based at least in part on the maximum TA.
 6. Themethod of claim 1, wherein determining whether to use the first timingconfiguration or the second timing configuration comprises: identifyinga maximum transport block size (TBS) available for the responsive uplinkcommunication; and determining to use either the first timingconfiguration or the second timing configuration based at least in parton the maximum TBS.
 7. The method of claim 1, further comprising:receiving control information associated with the downlink communicationin a control channel that spans an entire subframe; and determining touse the first timing configuration for the responsive uplinkcommunication based at least in part on the receiving.
 8. The method ofclaim 1, wherein a maximum transport block size (TBS) available foreither the first timing configuration or the second timing configurationis determined based at least in part on an indication of the capabilityof the UE to transmit the responsive uplink communication.
 9. The methodof claim 1, wherein a maximum transport block size (TBS) available foreither the first timing configuration or the second timing configurationis determined based at least in part on a number of concurrenttransmissions that may be received by the UE.
 10. The method of claim 1,further comprising: receiving radio resource control (RRC) signalingthat indicates the first timing configuration or the second timingconfiguration.
 11. The method of claim 1, wherein the responsive uplinkcommunication is a transmission of an asynchronous hybrid automaticrepeat request (HARQ) feedback associated with the PDSCH transmission.12. The method of claim 11, wherein a first number of HARQ processesassociated with the first timing configuration is greater than a secondnumber of HARQ processes associated with the second timingconfiguration.
 13. The method of claim 1, further comprising:identifying a periodicity for updating channel state information (CSI)based at least in part on the first timing configuration or the secondtiming configuration.
 14. The method of claim 1, further comprising:determining an aperiodic channel state information (CSI) configurationbased at least in part on a number of CSI processes supported for eitherthe first timing configuration or the second timing configuration. 15.The method of claim 1, further comprising: identifying a soundingreference signal (SRS) parameter based at least in part on either thefirst timing configuration or the second timing configuration.
 16. Themethod of claim 1, wherein the downlink communication is transmittedusing a set of component carriers, and wherein the first timingconfiguration is associated with a first subset of the set of componentcarriers and the second timing configuration is associated with a secondsubset of the set of component carriers.
 17. The method of claim 16,further comprising: configuring one or more of channel state information(CSI) reporting or hybrid automatic repeat request (HARQ) feedback forthe first subset of the set of component carriers based at least in parton the first timing configuration; and configuring one or more of CSIreporting or HARQ feedback for the second subset of the set of componentcarriers based at least in part on the second timing configuration. 18.An apparatus for wireless communication at a user equipment (UE),comprising: means for determining, based on a capability of the UE,whether to use a first timing configuration or a second timingconfiguration for transmissions, the first timing configurationincluding a first time difference between a downlink communication and aresponsive uplink communication, the downlink communication being aphysical downlink shared channel (PDSCH) transmission, the responsiveuplink communication being a physical uplink control channel (PUCCH)transmission, and the second timing configuration including a secondtime difference between the downlink communication and the responsiveuplink communication, the second time difference being less than thefirst time difference; and means for transmitting the responsive uplinkcommunication to the base station according to either the first timingconfiguration or the second timing configuration based on thedetermination.
 19. An apparatus for wireless communication at a userequipment (UE), in a system comprising: a processor; memory coupled withthe processor; and instructions stored in the memory and operable, whenexecuted by the processor, to cause the apparatus to: determine, basedon a capability of the UE, whether to use a first timing configurationor a second timing configuration for transmissions, the first timingconfiguration including a first time difference between a downlinkcommunication and a responsive uplink communication, the downlinkcommunication being a physical downlink shared channel (PDSCH)transmission, the responsive uplink communication being a physicaluplink control channel (PUCCH) transmission, and the second timingconfiguration including a second time difference between the downlinkcommunication and the responsive uplink communication, the second timedifference being less than the first time difference; and transmit theresponsive uplink communication to the base station according to eitherthe first timing configuration or the second timing configuration basedon the determination.
 20. The apparatus of claim 19, wherein theinstructions are further executable by the processor to cause theapparatus to: receive downlink control information (DCI) for thedownlink communication; and wherein the instructions executable by theprocessor to cause the apparatus to transmit according to the firsttiming configuration or the second timing configuration are furtherexecutable by the processor to cause the apparatus to transmit based atleast in part on a format of the DCI.
 21. The apparatus of claim 20,wherein the instructions executable by the processor to cause theapparatus to transmit according to the first timing configuration or thesecond timing configuration are further executable by the processor tocause the apparatus to: transmit according to the first timingconfiguration for a first subset of a set of available DCI formats; andtransmit according to the second timing configuration for a secondsubset of the set of available DCI formats.
 22. The apparatus of claim19, wherein the instructions executable by the processor to cause theapparatus to determine whether to use the first timing configuration orthe second timing configuration are further executable by the processorto cause the apparatus to: identify a maximum timing advance (TA)available for the responsive uplink communication; and determine to useeither the first timing configuration or the second timing configurationbased at least in part on the maximum TA.
 23. The apparatus of claim 19,wherein the instructions executable by the processor to cause theapparatus to determine whether to use the first timing configuration orthe second timing configuration are further executable by the processorto cause the apparatus to: identify a maximum transport block size (TBS)available for the responsive uplink communication; and determine to useeither the first timing configuration or the second timing configurationbased at least in part on the maximum TBS.
 24. The apparatus of claim19, wherein the instructions are further executable by the processor tocause the apparatus to: receive control information associated with thedownlink communication in a control channel that spans an entiresubframe; and determine to use the first timing configuration for theresponsive uplink communication based at least in part on the receiving.25. The apparatus of claim 19, wherein the instructions are furtherexecutable by the processor to cause the apparatus to: identify aperiodicity for updating channel state information (CSI) based at leastin part on the first timing configuration or the second timingconfiguration.
 26. The apparatus of claim 19, wherein the instructionsare further executable by the processor to cause the apparatus to:determine an aperiodic channel state information (CSI) configurationbased at least in part on a number of CSI processes supported for eitherthe first timing configuration or the second timing configuration. 27.The apparatus of claim 19, wherein the instructions are furtherexecutable by the processor to cause the apparatus to: identify asounding reference signal (SRS) parameter based at least in part oneither the first timing configuration or the second timingconfiguration.
 28. A non-transitory computer readable medium storingcode for wireless communication at a user equipment (UE), the codecomprising instructions executable by a processor to: determine, basedon a capability of the UE, whether to use a first timing configurationor a second timing configuration for transmissions, the first timingconfiguration including a first time difference between a downlinkcommunication and a responsive uplink communication, the downlinkcommunication being a physical downlink shared channel (PDSCH)transmission, the responsive uplink communication being a physicaluplink control channel (PUCCH) transmission, and the second timingconfiguration including a second time difference between the downlinkcommunication and the responsive uplink communication, the second timedifference being less than the first time difference; and transmit theresponsive uplink communication to the base station according to eitherthe first timing configuration or the second timing configuration basedon the determination.
 29. The method of claim 1, the capabilityincluding a capability of the UE to transmit the responsive uplinkcommunication within the first time difference or the second timedifference.
 30. The method of claim 29, the capability being signaled bythe UE to the base station.
 31. The method of claim 1, the determiningbeing further based on a timing difference of component carrierssupported by the UE.
 32. The method of claim 1, the responsive uplinkcommunication being transmitted over a PUCCH resource and multiplexedwith another uplink communication over the PUCCH resource.
 33. Themethod of claim 11, wherein determining whether to use the first timingconfiguration or the second timing configuration is further based on aradio resource control signaling.
 34. The method of claim 33, whereinthe capability of the UE comprises a processing capability.
 35. Theapparatus of claim 19, wherein the responsive uplink communication is atransmission of an asynchronous hybrid automatic repeat request (HARD)feedback associated with the PDSCH transmission.
 36. The apparatus ofclaim 35, wherein the determination to use either the first timingconfiguration or the second timing configuration is further based on aradio resource control signaling.
 37. The apparatus of claim 36, whereinthe capability of the UE comprises a processing capability.